Mathias FINK

Mathias FINK Professeur à l'ESPCI sur la chaire Georges Charpak Tél. : 01 80 96 30 69 Fax. : 01 80 96 33 55 Pièce : R51 Courriel :

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Je m’intéresse aux aspects les plus fondamentaux de la physique des ondes en milieu complexe et j’applique et valorise ces recherches aussi bien dans le domaine de l’imagerie que celui de la transmission d’informations. Mes recherches ont débouché sur de nombreuses applications qui vont de la médecine, à la défense, en passant par les télécommunications, la géophysique et l’interface homme-machine.

Après une thèse de 3° cycle en physique des solides, je me suis lancé dans l’aventure de l’imagerie médicale et mon travail de thèse d’Etat, auprès de Pierre Alais, a débouché sur la réalisation du premier échographe ultrasonore médical à haute résolution fonctionnant en temps réel (1978). En 1981, j’ai été nommé Professeur à l’Université de Strasbourg puis je suis parti comme professeur invité à l’Université d’Irvine dans le département de radiologie. De retour des USA, j’ai rejoint Paris où j’ai créé en 1990 à l’ESPCI le Laboratoire Ondes et Acoustique qui deviendra en 2009 l’Institut Langevin qui regroupe aujourd’hui une centaine de chercheurs sur la thématique « Ondes et Images ».

Mes recherches ont donné lieu à plusieurs découvertes et à la création de 6 sociétés innovantes (Echosens, Sensitive Object, Supersonic Imagine, Time-Reversal Communications, Cardiawave et GreenerWave) qui emploient près de 400 personnes. J’ai dirigé plus de 60 thèses et déposé plus de 70 brevets. Je suis l’auteur ou le co-auteur de plus de 400 articles scientifiques dans des revues avec comité de lecture. J’ai été le premier universitaire à être élu en 2008 comme Professeur au Collège de France sur la Chaire d’Innovation Technologique.

En exploitant les symétries de l’équation des ondes et l’arrivée dans les années 80 des premières mémoires électroniques rapides de grande capacité, j’ai proposé en 1987 le concept de « miroirs à retournement temporel » qui permet de faire revivre à une onde sa vie passée dans les milieux les plus complexes. Puis avec mon équipe, nous avons réalisé de tels miroirs pour différents types d’ondes (sonores, ultrasonores, sismiques, électromagnétiques, et vagues) et nous avons testé expérimentalement leur efficacité dans les milieux de propagation les plus variés. Le résultat le plus étonnant de cette recherche a été de montrer que, plus le milieu de propagation est complexe, plus il est facile de faire revivre à une onde sa vie passée. La complexité devient un atout et une unique antenne à « retournement temporel », immergée dans un milieu diffusant ou réverbérant, permet de focaliser une onde sur une tache dont la dimension ne dépend plus de la taille de l’antenne !! Ces résultats surprenants ont depuis été à l’origine de nombreuses recherches dans la communauté des mathématiciens, des opticiens et dans le domaine des télécommunications. Puis, avec Geoffroy Lerosey, Fabrice Lemoult, Julien de Rosny et Arnaud Tourin, nous avons montré, qu’on pouvait créer, par retournement temporel, des taches focales bien plus petites que la longueur d’onde en introduisant dans le milieu de propagation un matériau localement résonant structuré à une échelle sub-longueur d’onde (c’est le concept de « Resonant Metalens »).

Parallèlement à cette recherche sur les limites de la diffraction, j’ai exploré l’approche « retournement temporel » en imagerie, et avec ma collègue Claire Prada, nous avons introduit les concepts de retournement temporel itératif et d’opérateur de retournement temporel qui permettent de revisiter les techniques d’imagerie en milieu hétérogène en introduisant une approche matricielle de l’imagerie.

Avec mon équipe, j’ai valorisé ces concepts en développant de nombreuses applications comme :

• la réalisation d’un lithotripteur à retournement temporel qui traque et auto-focalise des ondes de choc ultrasonores uniquement sur les lithiases rénales et vésiculaires (avec Jean-Louis Thomas),
• un système de thérapie du cerveau par ultrasons qui permet de focaliser de façon optimale des ondes ultrasonores à travers la boite crânienne (avec Mickael Tanter et Jean-François Aubry),
• le développement d’objets tactiles intelligents faisant appel au retournement temporel des bruits générés par les impacts de doigts sur les objets (recherche conduite avec mon collègue Ros-Kiri Ing qui a créé la Société Sensitive Object vendue à TYCO),
• le développement de système de télécommunications électromagnétiques en milieu urbain ou dans des bâtiments par retournement temporel (avec Julien de Rosny, Geoffroy Lerosey et Arnaud Tourin : société Time-Reversal Communications vendue à ATOS),
• le développement de nouvelles méthodes de contrôle non-destructif pour l’Aéronautique (avec Claire Prada),
• le développement de radar et de sonar à retournement temporel pour voir derrière les murs ou pour détecter des objets dans les petits fonds marins (avec Claire Prada et Julien de Rosny).

Parallèlement aux recherches sur les miroirs à retournement temporel, j’ai initié et développé un deuxième thème de recherche dans le domaine de l’imagerie médicale : l’imagerie multi-ondes. J’ai introduit les concepts de « Transient Elastography » et de « Supersonic Shear Wave Imaging », deux méthodes qui permettent de réaliser des images quantitatives de l’élasticité des tissus en observant la propagation d’ondes de cisaillement BF à l’aide d’ultrasons. Ces recherches se sont concrétisés par la commercialisation de deux appareils très innovants : le Fibroscan et l’Aixplorer par deux des sociétés créées à partir de mon laboratoire : Echosens et Supersonic Imagine.

C’est d’abord dans le cadre des thèses de Stefan Catheline et de Laurent Sandrin que nous avons développé un premier appareil de mesure de l’élasticité qui a débouché en 2001 sur la création par Laurent Sandrin d’une première start-up ECHOSENS (140 personnes) qui commercialise le Fibroscan qui quantifie le degré de fibrose des pathologies hépatiques. Cet appareil connait un très grand succès international en hépatologie et est devenu le gold standard mondial dans la mesure du degré de fibrose. Plus de 5000 Fibroscans ont été installés dans le monde.

Puis, dans un deuxième temps, en combinant cette recherche avec la technologie des miroirs à retournement temporel, j’ai imaginé et, avec mon équipe, nous avons réalisé un appareil beaucoup plus sophistiqué, permettant d’obtenir des images quantitatives de l’élasticité des organes avec une précision millimétrique. Pour cela nous avons mis au point le premier imageur ultrasonore ultrarapide au monde (10.000 images/s) à partir duquel j’ai introduit le concept de « Shear Wave Elastography ». Avec Jacques Souquet, Jeremy Bercoff (mon thésard sur ce sujet), Mickael Tanter et Claude Cohen-Bacrie nous avons créé en 2005 la société SUPERSONIC IMAGINE qui compte aujourd’hui plus de 175 personnes. Supersonic Imagine commercialise depuis le début 2009 l’ « Aixplorer » qui a été vendu à plus de 2300 exemplaires dans le monde. Les applications de cette technologie sont très nombreuses : cancer du sein et de la thyroïde, cancer du foie, cancer de la prostate, maladie cardiovasculaire, pathologie musculo-squelettique, œil, peau...

Par la suite j’ai apporté de nombreuses améliorations au concept d’imagerie ultrarapide. La plus significative étant l’invention du mode « Coherent Plane-Wave Compounding » qui est désormais le gold standard en imagerie ultrarapide. J’ai aussi proposé et testé un nouveau mode d’imagerie que j’ai qualifié de BTI (Backscattering Tensor Imaging) et qui permet d’imager et de traquer par ultrasons la direction des fibres musculaires dans le cœur avec une résolution sub-millimétrique.

Parallèlement à ces applications médicales, je travaille actuellement sur plusieurs autres sujets.

Les uns concernent la physique des ondes la plus fondamentale avec le concept de « Miroir Temporel Instantané » que j’ai introduit récemment avec Emmanuel Fort et qui permet d’imaginer des « matériaux temporels » aux propriétés étonnantes revisitant à la fois les concepts d’holographie et la façon dont une antenne se couple à un milieu de propagation. Ces idées ont d’abord été vérifiées dans le domaine des vagues à la surface de l’eau et leur généralisation à la plasmonique et à la mécanique quantique motive beaucoup de groupes.

J’ai aussi initié, depuis une demi-douzaine d’années, une recherche sur les métasurfaces adaptatives. J’ai été ainsi à l’origine avec Geoffroy Lerosey du développement de « miroirs intelligents » pour les ondes électromagnétiques qui améliorent la qualité des communications dans les bâtiments en focalisant les ondes radio sur les téléphones portables (création en 2015 de la société GreenerWave). Récemment, j’ai généralisé ces idées dans le domaine du contrôle du son en développant des panneaux acoustiques modulables qui peuvent contrôler les ondes sonores dans une pièce bruitée pour créer, par exemple, une zone de silence à un endroit quelconque. Ces recherches ont données lieu à une intense collaboration avec l’Université de Hong Kong HKUST.

Je travaille aussi dans le cadre de l’ERC Synergy Helmholtz que j’ai obtenu en partenariat avec l’Institut de La Vison sur le développement de nouvelles méthodes d’imagerie optique en milieu diffusant (Smart OCT) utilisant le concept d’opérateur de retournement temporel. Ces approches que nous développons avec Alexandre Aubry et Claude Boccara permettent à la fois de multiplier par deux la profondeur d’inspection en microscopie optique et de corriger les aberrations optiques en exploitant la mesure de la matrice de réflexion optique. Les principales applications concernent l’œil. Dans le même ordre d’idée, J’ai proposé de mesurer et d’exploiter un nouveau type de matrice : la matrice de transfert acousto-optique pour imager des tissus diffuseurs en profondeur avec une résolution optique.

Enfin, avec mon collègue Ros Kiri Ing, je participe au développement du premier imageur ultrasonore sans contact des vibrations de la surface du corps humain qui devrait permettre de détecter des maladies cardio-respiratoires sans avoir a touché le patient.

Publications

Multi-spectral reflection matrix for ultrafast 3D label-free microscopy Balondrade, P., V. Barolle, N. Guigui, E. Auriant, N. Rougier, C. Boccara, M. Fink, and A. Aubry Nature Photonics 18, no. 10, 1097-1104 (2024) Résumé: Label-free microscopy exploits light scattering to obtain a three-dimensional image of biological tissues. However, light propagation is affected by aberrations and multiple scattering, which drastically degrade the image quality and limit the penetration depth. Multi-conjugate adaptive optics and time-gated matrix approaches have been developed to compensate for aberrations but the associated frame rate is extremely limited for three-dimensional imaging. Here we develop a multi-spectral matrix approach to solve these fundamental problems. On the basis of a sparse illumination scheme and an interferometric measurement of the reflected wave field at multiple wavelengths, the focusing process can be optimized in post-processing for any voxel by addressing independently each frequency component of the reflection matrix. A proof-of-concept experiment shows a three-dimensional image of an opaque human cornea over a 0.1 mm3 field of view at a 290 nm resolution and a 1 Hz frame rate. This work paves the way towards a fully digital microscope allowing real-time, in vivo, quantitative and deep inspection of tissues.
Matrix imaging as a tool for high-resolution monitoring of deep volcanic plumbing systems with seismic noise Giraudat, E., A. Burtin, A. Le Ber, M. Fink, J. C. Komorowski, and A. Aubry Communications Earth and Environment 5, no. 1 (2024) Résumé: Volcanic eruptions necessitate precise monitoring of magma pressure and inflation for improved forecasting. Understanding deep magma storage is crucial for hazard assessment, yet imaging these systems is challenging due to complex heterogeneities that disrupt standard seismic migration techniques. Here we map the magmatic and hydrothermal system of the La Soufrière volcano in Guadeloupe by analyzing seismic noise data from a sparse geophone array under a matrix formalism. Seismic noise interferometry provides a reflection matrix containing the signature of echoes from deep heterogeneities. Using wave correlations resistant to disorder, matrix imaging successfully unscrambles wave distortions, revealing La Soufrière’s internal structure down to 10 km with 100 m resolution. This method surpasses the diffraction limit imposed by geophone array aperture, providing crucial data for modeling and high-resolution monitoring. We see matrix imaging as a revolutionary tool for understanding volcanic systems and enhancing observatories’ abilities to monitor dynamics and forecast eruptions. (Figure presented.)
Harnessing forward multiple scattering for optical imaging deep inside an opaque medium Najar, U., V. Barolle, P. Balondrade, M. Fink, C. Boccara, and A. Aubry Nature Communications 15, no. 1 (2024) Résumé: As light travels through a disordered medium such as biological tissues, it undergoes multiple scattering events. This phenomenon is detrimental to in-depth optical microscopy, as it causes a drastic degradation of contrast, resolution and brightness of the resulting image beyond a few scattering mean free paths. However, the information about the inner reflectivity of the sample is not lost; only scrambled. To recover this information, a matrix approach of optical imaging can be fruitful. Here, we report on a de-scanned measurement of a high-dimension reflection matrix R via low coherence interferometry. Then, we show how a set of independent focusing laws can be extracted for each medium voxel through an iterative multi-scale analysis of wave distortions contained in R. It enables an optimal and local compensation of forward multiple scattering paths and provides a three-dimensional confocal image of the sample as the latter one had become digitally transparent. The proof-of-concept experiment is performed on a human opaque cornea and an extension of the penetration depth by a factor five is demonstrated compared to the state-of-the-art.
Tutorial: How to build and control an all-fiber wavefront modulator using mechanical perturbations Shekel, R., K. Sulimany, S. Resisi, Z. Finkelstein, O. Lib, S. M. Popoff, and Y. Bromberg Journal of Physics: Photonics 6, no. 3, 033002 (2024) Résumé: Multimode optical fibers support the dense, low-loss transmission of many spatial modes, making them attractive for technologies such as communications and imaging. However, information propagating through multimode fibers is scrambled, due to modal dispersion and mode mixing. This is usually rectified using wavefront shaping techniques with devices such as spatial light modulators. Recently, we demonstrated an all-fiber system for controlling light propagation inside multimode fibers using mechanical perturbations, called the fiber piano. In this tutorial we explain the design considerations and experimental methods needed to build a fiber piano, and review applications where fiber pianos have been used.
Solution to the cocktail party problem: A time-reversal active metasurface for multipoint focusing Bourdeloux, C., M. Fink, and F. Lemoult Physical Review Applied 21, no. 5, 054039 (2024) Résumé: The cocktail party effect is the capability to focus one's auditory attention on particular audio sources while ignoring other audio sources. We propose an experimental strategy to reproduce this ability by designing a time-dependent metasurface composed of independent active mirrors. Each active mirror is a programmable acoustic unit cell capable of hearing, computing, and re-emitting acoustic signals: each of them acts as a convolution filter. The proper configuration of the metasurface temporal filters allows one to establish an acoustic communication link between groups of individuals immersed in the noisy environment: a multiple-user multiple-input, multiple-output acoustic system is built. Mots-clés: metasurface;cocktail party;time reversal
Topology optimization for microwave control with reconfigurable intelligent metasurfaces in complex media Karamanos, T. D., M. Fink, and F. Lemoult Physical Review Applied 21, no. 4 (2024) Résumé: Reconfigurable intelligent metasurfaces have been proposed as an efficient solution for improving wireless telecommunication systems in multiple-scattering or reverberating media. Concurrently, topology optimization has been successfully used as an inverse-design technique in many fields, and particularly in electromagnetics. In this work, we apply a gradient-based topology optimization for tuning the binary elements of a metasurface for a focusing goal in a complex environment. First, the metasurface unit cells are approximated as point sources and, then, the optimization problem is formulated. Afterwards, the proposed method is applied to find the optimal parameter sets for three distinct environments of increasing complexity, and the resulting focus for each case is demonstrated via numerical simulations. The combination of a reverberating cavity and a metasurface inside the latter is very powerful since everything can be solved analytically for focusing outside the cavity.
Airborne ultrasound for the contactless mapping of surface thoracic vibrations during human vocalizations: A pilot study Wintzenrieth, F., M. Couade, F. Lehanneur, P. Laveneziana, M. C. Niérat, N. Verger, M. Fink, T. Similowski, and R. K. Ing AIP Advances 14, no. 3 (2024) Résumé: Physical examination of the thorax is key to the clinical diagnosis of respiratory diseases. Among other examination techniques, palpation evaluates the transmission of high-frequency vibrations produced by vocalizations (tactile fremitus), which helps the physicians to identify abnormalities within the respiratory system. We propose the use of an airborne ultrasound surface motion camera (AUSMC) to quantitatively map the vibrations induced by subject vocalization. This approach could make the examination of vocal fremitus quantifiable, reproducible, and archivable. Massive data collection of vocal fremitus could allow using artificial intelligence algorithms to isolate vibration patterns that could help disease identification. Until now, in contrast, the interpretation of vocal fremitus has been subject to the physician’s experience and remains subjective. In the present work, we demonstrate the capabilities of the AUSMC to measure vocal fremitus thoracic vibration maps on 77 healthy volunteers. We have observed a spatial dependence of vibration maps on vocalization frequency. We observed that the left lung generates fewer surface vibrations than the right one, which was expected according to their respective dimensions. We also discuss the implications of our findings.
Optimizing multi-user indoor sound communications with acoustic reconfigurable metasurfaces Zhang, H., Q. Wang, M. Fink, and G. Ma Nature Communications 15, no. 1, 1270 (2024) Résumé: Sound in indoor spaces forms a complex wavefield due to multiple scattering encountered by the sound. Indoor acoustic communication involving multiple sources and receivers thus inevitably suffers from cross-talks. Here, we demonstrate the isolation of acoustic communication channels in a room by wavefield shaping using acoustic reconfigurable metasurfaces (ARMs) controlled by optimization protocols based on communication theories. The ARMs have 200 electrically switchable units, each selectively offering 0 or π phase shifts in the reflected waves. The sound field is reshaped for maximal Shannon capacity and minimal cross-talk simultaneously. We demonstrate diverse acoustic functionalities over a spectrum much larger than the coherence bandwidth of the room, including multi-channel, multi-spectral channel isolations, and frequency-multiplexed acoustic communication. Our work shows that wavefield shaping in complex media can offer new strategies for future acoustic engineering.
A non-linear delayed resonator for mimicking the hearing haircells Reda, J., M. Fink, and F. Lemoult Europhysics Letters 144, no. 3, 37001 (2023)
Three-dimensional ultrasound matrix imaging Bureau, F., J. Robin, A. Le Ber, W. Lambert, M. Fink, and A. Aubry Nature Communications 14, no. 1 (2023) Résumé: Matrix imaging paves the way towards a next revolution in wave physics. Based on the response matrix recorded between a set of sensors, it enables an optimized compensation of aberration phenomena and multiple scattering events that usually drastically hinder the focusing process in heterogeneous media. Although it gave rise to spectacular results in optical microscopy or seismic imaging, the success of matrix imaging has been so far relatively limited with ultrasonic waves because wave control is generally only performed with a linear array of transducers. In this paper, we extend ultrasound matrix imaging to a 3D geometry. Switching from a 1D to a 2D probe enables a much sharper estimation of the transmission matrix that links each transducer and each medium voxel. Here, we first present an experimental proof of concept on a tissue-mimicking phantom through ex-vivo tissues and then, show the potential of 3D matrix imaging for transcranial applications.
Subwavelength pulse focusing and perfect absorption in the Maxwell fish-eye Lefebvre, G., M. Dubois, Y. Achaoui, R. K. Ing, M. Fink, S. Guenneau, and P. Sebbah Applied Physics Letters 123, no. 13 (2023) Résumé: Maxwell's fish-eye is a paradigm for an absolute optical instrument with a refractive index deduced from the stereographic projection of a sphere on a plane. We investigate experimentally the dynamics of flexural waves in a thin plate with a thickness varying according to the Maxwell fish-eye index profile and a clamped boundary. We demonstrate subwavelength focusing and temporal pulse compression at the image point. This is achieved by introducing a sink emitting a cancelling signal optimally shaped using a time-reversal procedure. Perfect absorption and outward going wave cancellation at the focus point are demonstrated. The time evolution of the kinetic energy stored inside the cavity reveals that the sink absorbs energy out of the plate ten times faster than the natural decay rate.
Measuring Dirac cones in a brick-wall lattice microwave metamaterial Li, B., S. Yves, A. Delory, S. Liu, M. Fink, and F. Lemoult Physical Review B 108, no. 9 (2023) Résumé: The intriguing discovery of bidimensional structures in solid-state physics has motivated the seeking of their analogs in many fields. In this paper, we propose a general scheme to achieve Dirac cones in the microwave domain. It is based on a bidimensional locally resonant metamaterial ruled by a tight-binding Hamiltonian with asymmetric coupling. By specifically controlling the hopping links between meta-atoms, the Dirac cones can be moved in the first Brillouin zone. A proof of this assertion is performed theoretically, numerically, and experimentally using a brick-wall lattice of resonant metallic wires. The results directly evidence that the crystalline description of a subwavelength-scaled microwave system provides a really convenient tabletop platform for investigating the tempting challenges offered in solid-state physics.
Dynamic full-field optical coherence tomography of retinal pigment epithelium cell cultures to model degenerative diseases Groux, K., J. Scholler, A. Verschueren, M. Darche, L. Boucherit, P. Mecê, V. Fradot, J.-M. Chassot, M. Fink, S. Reichman, M. Paques, C. Boccara, O. Thouvenin, and K. Grieve Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXV (2021) Résumé: Dynamic FFOCT allows us to record the intrinsic motion of biological samples in 3D, over hours. We performed scratch assays on primary porcine RPE and human induced pluripotent stem cells derived RPE cell cultures. We plotted motion maps from the optical flow. For wounds <40µm, the cell layer close the wound at different speeds depending on the type of RPE cells. For bigger wounds, the cell layer retract, mimicking degenerative diseases. Comparison between Dynamic FFOCT images and Immuno-chemistry images showed that mitochondria may contribute to the dynamic profile of cells. Dynamic FFOCT can be useful for the study of regenerative medicine.
Compact Metamaterial Antenna for Angular Localization of Radio-frequency Sources Ourir, A., M. Kamoun, A. Tourin, M. Fink, and J. De Rosny 17th European Conference on Antennas and Propagation, EuCAP 2023 (2023) Résumé: Localization of radio-frequency sources is commonly carried out by adjusting the radiation patterns of phased arrays to scan a specific region. This task could be difficult and expensive to implement in some frequency regimes of the last generation of communication systems. We present an alternative to the classical Radio-frequency angular localization based on a single port compact metamaterial antenna. We use a finite periodic array of sub-wavelength (λ/6) resonators for the design of this antenna. We show that the proposed antenna is able to achieve several complex radiation patterns over a specific narrow frequency band. We implement numerical methods to estimate the direction of a target antenna by taking benefits of the complex frequency signatures over this band. We demonstrate experimentally in the microwave regime that a single port antenna made of a finite array of metamaterial resonators can be used to retrieve the incident direction.
The Aharonov-Bohm Effect Revisited by an Acoustic Time-Reversal Mirror Roux, P., J. De Rosny, M. Tanter, and M. Fink Physical Review Letters 79, no. 17, 3170-3173 (1997)
Reversible Hardware for Acoustic Communications Siljak, H., J. d. Rosny, and M. Fink IEEE Communications Magazine 58, no. 1, 55-61 (2020)
Reconfigurable Intelligent Surfaces vs. Relaying: Differences, Similarities, and Performance Comparison Di Renzo, M., K. Ntontin, J. Song, F. H. Danufane, X. Qian, F. Lazarakis, J. De Rosny, D.-T. Phan-Huy, O. Simeone, R. Zhang, M. Debbah, G. Lerosey, M. Fink, S. Tretyakov, and S. Shamai IEEE Open Journal of the Communications Society 1, 798-807 (2020)
Experimental Validation of Time Reversal Multiple Access for UWB Wireless Communications Centered at the 273 GHz Frequency Mokh, A., J. De Rosny, G. C. Alexandropoulos, M. Kamoun, A. Ourir, R. Khayatzadeh, A. Tourin, and M. Fink 2022 IEEE 95th Vehicular Technology Conference: (VTC2022-Spring), 1-5 (2022)
Time Reversal for 6G Spatiotemporal Focusing: Recent Experiments, Opportunities, and Challenges Alexandropoulos, G. C., A. Mokh, R. Khayatzadeh, J. De Rosny, M. Kamoun, A. Ourir, A. Tourin, M. Fink, and M. Debbah IEEE Vehicular Technology Magazine 17, no. 4, 74-82 (2022)
Maximizing Focus Quality Through Random Media with Discrete-Phase-Sampling Lenses Wang, Q., M. Fink, and G. Ma Physical Review Applied 19, no. 3 (2023) Résumé: Wavefronts modulated by a discrete-phase-sampling lens, such as a spatial light modulator or a digital micromirror device, can be brought into focus after propagating through a random medium. Such techniques are a cornerstone for wave manipulations in multiple scattering environments. In this work, we examine prevailing focusing protocols, including matched filtering and inverse filtering, from the perspective of focus quality, which is defined as the contrast between the energy delivered to the focal peak and the total transmitted energy. Our results show that conventional protocols have limitations in achieving the best focus quality. Based on these analyses, we present an improved wavefront-shaping protocol that directly prioritizes focus quality. The influence of phase sampling resolutions is also analyzed in conjunction with these focusing protocols. Our results can merit the future design and implementation of intelligent lenses, which may potentially benefit various disciplines such as energy delivery, imaging, and communication.
Compressive sensing-based correlation sidelobe suppression for passive water pipeline fault detection using ambient noise Li, Z., P. Lee, M. Fink, R. Murch, and M. Davidson Mechanical Systems and Signal Processing 195, 110323 (2023) Résumé: The ambient noise in water pipelines are observed as spontaneous signal sources that can be used for pipe fault detection by correlation analysis. However, the limited bandwidth of these noise signal causes strong correlation sidelobes, which introduces significant ambiguities when extracting the system response from correlation results and this increases the risk of false alarms from fault detections. This paper proposes a compressive sensing based method that can extend the noise bandwidth and suppress the correlation sidelobes. Numerical and field experiment results have shown that with the recovered wider bandwidth, the correlation sidelobes can be significantly suppressed and the pipe faults can be identified with greater certainty. The impacts of fault size as well as noise bandwidth, strength and spectrum features on the proposed method are also assessed through numerical experiments.
Damping-Driven Time Reversal for Waves Hidalgo-Caballero, S., S. Kottigegollahalli Sreenivas, V. Bacot, S. Wildeman, M. Harazi, X. Jia, A. Tourin, M. Fink, A. Cassinelli, M. Labousse, and E. Fort Physical Review Letters 130, no. 8 (2023) Résumé: Damping is usually associated with irreversibility. Here, we present a counterintuitive concept to achieve time reversal of waves propagating in a lossless medium using a transitory dissipation pulse. Applying a sudden and strong damping in a limited time generates a time-reversed wave. In the limit of a high damping shock, this amounts to "freezing"the initial wave by maintaining the wave amplitude while canceling its time derivative. The initial wave then splits in two counterpropagating waves with half of its amplitude and time evolutions in opposite directions. We implement this damping-based time reversal using phonon waves propagating in a lattice of interacting magnets placed on an air cushion. We show with computer simulations that this concept also applies to broadband time reversal in complex disordered systems.
Superresolved Imaging Based on Spatiotemporal Wave-Front Shaping Noetinger, G., S. Métais, G. Lerosey, M. Fink, S. M. Popoff, and F. Lemoult Physical Review Applied 19, no. 2 (2023) Résumé: A label-free approach to improving the performances of confocal scanning imaging is proposed. We experimentally demonstrate its feasibility using acoustic waves. It relies on a way to encode spatial information using the temporal dimension. By moving an emitter, used to insonify an object, along a circular path, we create a temporally modulated wavefield. Because of the symmetries of the problem, the spatiotemporal input field can be decomposed into harmonics corresponding to different spatial vortices. Acquiring the back-reflected waves with receivers that are also rotating, multiple images of the same object with different point spread functions are obtained. Not only is the resolution improved compared to a standard confocal configuration, but the accumulation of information also allows the building of images that beat the diffraction limit.
Ultrasound Matrix Imaging - Part II: The Distortion Matrix for Aberration Correction Over Multiple Isoplanatic Patches Lambert, W., L. A. Cobus, J. Robin, M. Fink, and A. Aubry IEEE Transactions on Medical Imaging 41, no. 12, 3921-3938 (2022) Résumé: This is the second article in a series of two which report on a matrix approach for ultrasound imaging in heterogeneous media. This article describes the quantification and correction of aberration, i.e. the distortion of an image caused by spatial variations in the medium speed-of-sound. Adaptive focusing can compensate for aberration, but is only effective over a restricted area called the isoplanatic patch. Here, we use an experimentally-recorded matrix of reflected acoustic signals to synthesize a set of virtual transducers. We then examine wave propagation between these virtual transducers and an arbitrary correction plane. Such wave-fronts consist of two components: (i) An ideal geometric wave-front linked to diffraction and the input focusing point, and; (ii) Phase distortions induced by the speed-of-sound variations. These distortions are stored in a so-called distortion matrix, the singular value decomposition of which gives access to an optimized focusing law at any point. We show that, by decoupling the aberrations undergone by the outgoing and incoming waves and applying an iterative strategy, compensation for even high-order and spatially-distributed aberrations can be achieved. After a numerical validation of the process, ultrasound matrix imaging (UMI) is applied to the in-vivo imaging of a gallbladder. A map of isoplanatic modes is retrieved and is shown to be strongly correlated with the arrangement of tissues constituting the medium. The corresponding focusing laws yield an ultrasound image with drastically improved contrast and transverse resolution. UMI thus provides a flexible and powerful route towards computational ultrasound.
Ultrasound Matrix Imaging - Part I: The Focused Reflection Matrix, the F-Factor and the Role of Multiple Scattering Lambert, W., J. Robin, L. A. Cobus, M. Fink, and A. Aubry IEEE Transactions on Medical Imaging 41, no. 12, 3907-3920 (2022) Résumé: This is the first article in a series of two dealing with a matrix approach for aberration quantification and correction in ultrasound imaging. Advanced synthetic beamforming relies on a double focusing operation at transmission and reception on each point of the medium. Ultrasound matrix imaging (UMI) consists in decoupling the location of these transmitted and received focal spots. The response between those virtual transducers form the so-called focused reflection matrix that actually contains much more information than a confocal ultrasound image. In this paper, a time-frequency analysis of this matrix is performed, which highlights the single and multiple scattering contributions as well as the impact of aberrations in the monochromatic and broadband regimes. Interestingly, this analysis enables the measurement of the incoherent input-output point spread function at any pixel of this image. A fitting process enables the quantification of the single scattering, multiple scattering and noise components in the image. From the single scattering contribution, a focusing criterion is defined, and its evolution used to quantify the amount of aberration throughout the ultrasound image. In contrast to the state-of-the-art coherence factor, this new indicator is robust to multiple scattering and electronic noise, thereby providing a contrasted map of the focusing quality at a much better transverse resolution. After a validation of the proof-of-concept based on time-domain simulations, UMI is applied to the in-vivo study of a human calf. Beyond this specific example, UMI opens a new route for speed-of-sound and scattering quantification in ultrasound imaging.
Passive Measurement of Pressure Wave Speed in Water Pipelines Using Ambient Noise Li, Z., P. Lee, M. Fink, and R. Murch Mechanisms and Machine Science 125 MMS, 1077-1084 (2023) Résumé: The wave speed of pressure waves in water pipelines is sensitive to the reduction in pipe wall thickness and material strength, and it has been utilized as an indicator of water pipeline deterioration. These probing pressure waves are usually generated actively and is challenging to be incorporated into an automated senor network. This paper proposed a passive wave speed estimation method, which takes cross-correlation of the ambient noise in water pipeline networks measured by two synchronized pressure sensors to estimate the wave travel time. Field experiments were carried out in the operating water reticulation system at University of Canterbury campus for validation. In the experiments, pressure sensors were attached to fire hydrants to measure the ambient noise for 20 min. The experiment results indicate that pressure wave speed can be estimated using the proposed passive method, and the accuracy is at the same level compared with the conventional active method.
Wavefront Shaping for Wireless Communications in Complex Media: From Time Reversal to Reconfigurable Intelligent Surfaces Lerosey, G., and M. Fink Proceedings of the IEEE 110, no. 9, 1210-1226 (2022) Résumé: Reconfigurable intelligent surfaces (RISs) are gaining huge momentum in the field of wireless communications due to the paradigm shift that they bring. Indeed, they allow making any environment electromagnetically smart and dynamically reconfigurable for more efficient and greener wireless communications. As physicists, we proposed to use electronically tunable metasurfaces to shape the electromagnetic waves carrying our wireless communications in reflection almost ten years ago, inspired by some works that we and colleagues did in the field of wave control in complex media. In this article, we review the seminal works that led us to propose this concept, starting from the original one that is time reversal. Then, we propose a physicist's point of view of RISs using a comparison with phase conjugation. Finally, we highlight what we think are their limitations, relying on both our knowledge of wave control and our study of them over a decade.
Passive detection in water pipelines using ambient noise II: Field experiments Li, Z., P. Lee, M. Fink, R. Murch, and M. Davidson Mechanical Systems and Signal Processing 181, 109524 (2022) Résumé: A passive detection method has been proposed in a prior paper to extract key parameters and detect faults using the ambient noise present in water pipeline networks. This paper presents field experiments and data processing results to provide systematic experimental validation of this method. Field experiments were carried out in operational water pipeline networks at the University of Canterbury campus and the Waimakariri District, New Zealand, during which ambient noise was measured by pairs of pressure sensors installed at selected hydrants on pipelines of different materials, network topologies and simulated faults. Auto-correlation and cross-correlation analysis of noise at a single sensor and sensor pairs were carried out to estimate the wave speed and to locate faults in the networks. Data processing results indicate that water usage generating pressure transients are the dominant sources of ambient noise in operational water pipeline networks. This type of ambient noise can also be utilized by the passive detection method to achieve similar wave speed estimation accuracy and fault detection performance as the conventional active pressure wave detection methods.
Dynamic full-field optical coherence tomography allows live imaging of retinal pigment epithelium stress model Groux, K., A. Verschueren, C. Nanteau, M. Clémençon, M. Fink, J.-A. Sahel, C. Boccara, M. Paques, S. Reichman, and K. Grieve Communications Biology 5, no. 1 (2022)
Time Reversal for Multiple Access and Mobility: Algorithmic Design and Experimental Results Mokh, A., J. De Rosny, G. C. Alexandropoulos, R. Khayatzadeh, M. Kamoun, A. Ourir, A. Tourin, and M. Fink IEEE Wireless Communications and Networking Conference, WCNC 2022-April, 1731-1736 (2022) Résumé: Time Reversal (TR) has been proposed as a competitive precoding strategy for low-complexity wireless devices relying on Ultra-WideBand (UWB) signal waveforms. However, when TR is applied for multiple access, the signals received by the multiple users suffer from significant levels of inter-symbol and inter-user interference, which requires additional processing for mitigation by each receiving user. In this paper, we present an iterative Time-Reversal Division Multiple Access (TRDMA) approach that aims to dim the latter interference levels. The performance of iterative TRDMA is evaluated experimentally in a reverberation chamber that mimics a rich scattering indoor wireless propagation environment. The improved efficiency, in terms of the number of algorithmic iterations, of the proposed approach compared to conventional TRDMA, is demonstrated. We also consider a mobile user configuration, where the position of the receiver changes between the channel estimation and data transmission steps. It is showcased, even for this experimental setup, that the proposed iterative TRDMA approach is more efficient than conventional precoding schemes.
Time-reversal of Sub-THz Pulses in Complex Media Mokh, A., R. Khayatzadeh, A. Ourir, M. Kamoun, A. Tourin, M. Fink, and J. De Rosny Progress In Electromagnetics Research B 95, 141-162 (2022) Résumé: Abstract|For the last 20 years, the time-reversal (TR) process has been successfully applied to focus pulses in the microwave frequency range and in complex media. Here we examine the specic conditions to obtain the same results but in the sub-THz frequency range. Because of the stronger attenuation at this much higher frequency, it is more challenging to exploit the TR self-focusing property. The TR of pulses is studied in two kinds of complex media: metallic waveguide and leaky reverberating cavity. For each medium, we propose one or two models to assess the quality of the focusing. For the waveguide, we show that the angle of incidence is an important parameter. Based on these results, we perform TR experiments at 273 GHz with a bandwidth that can be as large as 2 GHz. TR experiments are successfullyrst conducted in a 1m long and 10mm diameter straight hollow cylinder and then in a 5m long and 12mm diameter curved waveguide. Finally, we present results obtained in a cavity of 72 cm3 that leaks through a copper grid. The best focusing is observed with the longer waveguide.
Freeze-Dried Microfluidic Monodisperse Microbubbles as a New Generation of Ultrasound Contrast Agents Soysal, U., P. N. Azevedo, F. Bureau, A. Aubry, M. S. Carvalho, A. C. S. N. Pessoa, L. G. D. L. Torre, O. Couture, A. Tourin, M. Fink, and P. Tabeling Ultrasound in Medicine and Biology (2022) Résumé: We succeeded in freeze-drying monodisperse microbubbles without degrading their performance, that is, their monodispersity in size and echogenicity. We used microfluidic technology to generate cryoprotected highly monodisperse microbubbles (coefficient of variation [CV] <5%). By using a novel retrieval technique, we were able to freeze-dry the microbubbles and resuspend them without degradation, that is, keeping their size distribution narrow (CV <6%). Acoustic characterization performed in two geometries (a centimetric cell and a millichannel) revealed that the resuspended bubbles conserved the sharpness of the backscattered resonance peak, leading to CVs ranging between 5% and 10%, depending on the geometry. As currently observed with monodisperse bubbles, the peak amplitudes are one order of magnitude higher than those of commercial ultrasound contrast agents. Our work thus solves the question of storage and transportation of highly monodisperse bubbles. This work might open pathways toward novel clinical non-invasive measurements, such as local pressure, impossible to carry out with the existing commercial ultrasound contrast agents.
Static-to-dynamic field conversion with time-varying media Mencagli, M. J., D. L. Sounas, M. Fink, and N. Engheta Physical Review B 105, no. 14 (2022) Résumé: We theoretically demonstrate that a uniform static electric field distribution can be partially converted to radiation fields when a portion of the medium undergoes a temporal change of its permittivity. An in-depth theoretical investigation of this phenomenon is developed for a dielectric block with a steplike temporal change located inside a waveguide charged with a DC voltage source. Closed analytical expressions are derived for the radiated electric and magnetic fields. The exchange of energy between the electrostatic and electromagnetic fields is discussed. The reconciliation between the seemingly contradictory temporal and spatial boundary conditions for the electric and magnetic fields at the interface of the time-varying dielectric block is analyzed and elucidated. Our findings may provide an alternative solution for generating electromagnetic radiation based on time-varying media.
Optical phase modulation by natural eye movements: application to time-domain FF-OCT image retrieval Mazlin, V., P. Xiao, K. Irsch, J. Scholler, K. Groux, K. Grieve, M. Fink, and A. C. Boccara Biomedical Optics Express 13, no. 2, 902-920 (2022) Résumé: Eye movements are commonly seen as an obstacle to high-resolution ophthalmic imaging. In this context we study the natural axial movements of the in vivo human eye and show that they can be used to modulate the optical phase and retrieve tomographic images via time-domain full-field optical coherence tomography (TD-FF-OCT). This approach opens a path to a simplified ophthalmic TD-FF-OCT device, operating without the usual piezo motor-camera synchronization. The device demonstrates in vivo human corneal images under the different image retrieval schemes (2-phase and 4-phase) and different exposure times (3.5 ms, 10 ms, 20 ms). Data on eye movements, acquired with a spectral-domain OCT with axial eye tracking (180 B-scans/s), are used to study the influence of ocular motion on the probability of capturing high-signal tomographic images without phase washout. The optimal combinations of camera acquisition speed and amplitude of piezo modulation are proposed and discussed.
Unidirectional amplification with acoustic non-Hermitian space−time varying metamaterial Wen, X., X. Zhu, A. Fan, W. Y. Tam, J. Zhu, H. W. Wu, F. Lemoult, M. Fink, and J. Li Communications Physics 5, no. 1 (2022) Résumé: Space−time modulated metamaterials support extraordinary rich applications, such as parametric amplification, frequency conversion, and non-reciprocal transmission. The non-Hermitian space−time varying systems combining non-Hermiticity and space−time varying capability, have been proposed to realize wave control like unidirectional amplification, while its experimental realization still remains a challenge. Here, based on metamaterials with software-defined impulse responses, we experimentally demonstrate non-Hermitian space−time varying metamaterials in which the material gain and loss can be dynamically controlled and balanced in the time domain instead of spatial domain, allowing us to suppress scattering at the incident frequency and to increase the efficiency of frequency conversion at the same time. An additional modulation phase delay between different meta-atoms results in unidirectional amplification in frequency conversion. The realization of non-Hermitian space−time varying metamaterials will offer further opportunities in studying non-Hermitian topological physics in dynamic and nonreciprocal systems.
Gravitational lens effect revisited through membrane waves Catheline, S., V. Delattre, G. Laloy-Borgna, F. Faure, and M. Fink American Journal of Physics 90, no. 1, 47-50 (2022) Résumé: By means of experiments and curved manifold simulations, we show that wave propagation past a topological deviation on a two-dimensional flat fabric membrane is analogous to gravitational lensing. Using an ultrafast camera, we track a membrane plane wave as it crosses a local warped depression. Finite difference simulation, based on the scalar wave equation in a Schwarzschild metric, fully describes the experimental wavefront shape. Comparison between the theoretical and experimental deviation of wave geodesics from straight lines shows that (i) the nonlinear behavior of fabrics due to stretching induces second order effects only and (ii) the experimental depression is closely approximated by the Schwarzschild metric of a gravity well. The experiment demonstrates, in a simple way, how wave propagation is influenced by the topology of the transmission medium.
Negative Transient Flux in the near Field of a Subwavelength Source Li, X., P. Li, M. H. Lu, M. Fink, and G. Ma Physical Review Applied 16, no. 1 (2021) Résumé: The emission of waves by a small source is a generic wave problem that has long been thought to be well studied. Here, we report the experimental observation that the energy flux of an outgoing sound wave emitted by a deep-subwavelength-sized source can become negative, which indicates the backward flow of energy. Such a negative transient flux exists, even in a homogenous medium, but is only observable in the time domain and in the extreme near field of the source. By wave-impedance analysis, we show that such a phenomenon is fundamentally rooted in the geometry of the wavefield itself and, hence, is generic. Our findings have implications in the time-dependent emission, absorption, and scattering of waves.
Fourier transform acousto-optic imaging with off-axis holographic detection Dutheil, L., M. Bocoum, M. Fink, S. M. Popoff, F. Ramaz, and J. M. Tualle Applied Optics 60, no. 24, 7107-7112 (2021) Résumé: Acousto-optic (AO) imaging is an in-depth optical imaging technique of highly scattering media. One challenging end-application for this technique is to perform imaging of living biological tissues. Indeed, because it relies on coherent illumination, AO imaging is sensitive to speckle decorrelation occurring on the millisecond time scale. Camera-based detections are well suited for in vivo imaging provided their integration time is lower than those decorrelation time scales. We present Fourier transform acousto-optic imaging combined with off-axis holography, which relies on plane waves and long-duration pulses. We demonstrate, for the first time to the best of our knowledge, a two-dimensional imaging system fully compatible with in vivo imaging prerequisites. The method is validated experimentally by performing in-depth imaging inside a multiple scattering sample.
Indoor Experimental Evaluation of Ultra-wideband MU-MISO TRDMA Mokh, A., R. Khayatzadeh, J. De Rosny, M. Kamoun, A. Ourir, M. Fink, and A. Tourin IEEE Vehicular Technology Conference 2021-April (2021) Résumé: MISO Time-Reversal (TR) communication marks a paradigm shift for ultrawideband (UWB) communications because the processing is mainly carried out by the transmitter, which is ideal for some applications. Thanks to its focusing property, TR is naturally dedicated to multiple access trans-mission (TRDMA). Previous research works have focused on the theoretical performance of TRDMA. In this paper, Multi-user MISO (MU-MISO) TRDMA transmission is evaluated experimentally for the first time to the best of our knowledge, and by simulations. An experimental setup is used to measure the TRDMA signals for different bandwidth in multi-user scenario. The experimental results are then used in a simulation to evaluate the bit error rate and the performance of the system.
Manifestation of aberrations in full-field optical coherence tomography Barolle, V., J. Scholler, P. Mecê, J. M. Chassot, K. Groux, M. Fink, A. C. Boccara, and A. Aubry Optics Express 29, no. 14, 22044-22065 (2021) Résumé: We report on a theoretical model for image formation in full-field optical coherence tomography (FFOCT). Because the spatial incoherence of the illumination acts as a virtual confocal pinhole in FFOCT, its imaging performance is equivalent to a scanning time-gated coherent confocal microscope. In agreement with optical experiments enabling a precise control of aberrations, FFOCT is shown to have nearly twice the resolution of standard imaging at moderate aberration level. Beyond a rigorous study on the sensitivity of FFOCT with respect to aberrations, this theoretical model paves the way towards an optimized design of adaptive optics and computational tools for high-resolution and deep imaging of biological tissues.
Passive imaging of water pipelines using ambient turbulence noise Wang, W., Z. Li, A. Dubey, P. Lee, M. Fink, and R. Murch Mechanical Systems and Signal Processing 160 (2021) Résumé: Ambient noise generated by flowing water turbulence is harnessed as a signal source for imaging key parameters and fault detection in water pipelines. This approach is important because it can aid in the estimation of wave speed or detection of water pipeline defects such as blockages and leakages. More importantly it overcomes the challenging problem of generating a signal source of sufficient power to provide the necessary signal-to-noise ratios for conventional water pipeline imaging and fault detection techniques. In this paper, the expressions of the auto- and cross-correlation functions of the ambient noise between sensors are derived using wave theory. It is shown that the time-domain Green's functions can be extracted from the correlation functions. Experimental and numerical examples are provided for water pipelines to demonstrate that wave speed can be estimated from the time-domain Green's functions. A method for extending the technique, by using straightforward but accurate approximations of the correlation functions, to detect the presence of defects in the profile of the water pipeline is also proposed.
Coherence gate shaping for wide field high-resolution in vivo retinal imaging with full-field OCT Mecê, P., K. Groux, J. Scholler, O. Thouvenin, M. Fink, K. Grieve, and C. Boccara Biomedical Optics Express 11, no. 9, 4928-4941 (2020) Résumé: © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement Allying high-resolution with a large field-of-view (FOV) is of great importance in the fields of biology and medicine, but it is particularly challenging when imaging non-flat living samples such as the human retina. Indeed, high-resolution is normally achieved with adaptive optics (AO) and scanning methods, which considerably reduce the useful FOV and increase the system complexity. An alternative technique is time-domain full-field optical coherence tomography (FF-OCT), which has already shown its potential for in-vivo high-resolution retinal imaging. Here, we introduce coherence gate shaping for FF-OCT, to optically shape the coherence gate geometry to match the sample curvature, thus achieving a larger FOV than previously possible. Using this instrument, we obtained high-resolution images of living human photoreceptors close to the foveal center without AO and with a 1 mm × 1 mm FOV in a single shot. This novel advance enables the extraction of photoreceptor-based biomarkers with ease and spatiotemporal monitoring of individual photoreceptors. We compare our findings with AO-assisted ophthalmoscopes, highlighting the potential of FF-OCT, as a compact system, to become a routine clinical imaging technique.
Curved-field optical coherence tomography: Large-field imaging of human corneal cells and nerves Mazlin, V., K. Irsch, M. Paques, J. A. Sahel, M. Fink, and C. A. Boccara Optica 7, no. 8, 872-880 (2020) Résumé: © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement Cell-resolution optical imaging methods, such as confocal microscopy and full-field optical coherence tomography, capture flat optical sections of the sample. If the sample is curved, the optical field sections through several sample layers, and the view of each layer is reduced. Here we present curved-field optical coherence tomography, capable of capturing optical sections of arbitrary curvature. We test the device on a challenging task of imaging the human cornea in vivo and achieve a 10× larger viewing area comparing to the clinical state-of-the-art. This enables more precise cell and nerve counts, opening a path to improved monitoring of corneal and general health conditions (e.g., diabetes). The method is non-contact, compact, and works in a single fast shot (3.5 ms), making it readily available for use in optical research and clinical practice.
Reflection Matrix Approach for Quantitative Imaging of Scattering Media Lambert, W., L. A. Cobus, M. Couade, M. Fink, and A. Aubry Physical Review X 10, no. 2 (2020) Résumé: © 2020 authors. Published by the American Physical Society. We present a physically intuitive matrix approach for wave imaging and characterization in scattering media. The experimental proof of concept is performed with ultrasonic waves, but this approach can be applied to any field of wave physics for which multielement technology is available. The concept is that focused beam forming enables the synthesis, in transmit and receive, of an array of virtual transducers which map the entire medium to be imaged. The interelement responses of this virtual array form a focused reflection matrix from which spatial maps of various characteristics of the propagating wave can be retrieved. Here we demonstrate (i) a local focusing criterion that enables the image quality and the wave velocity to be evaluated everywhere inside the medium, including in random speckle, and (ii) a highly resolved spatial mapping of the prevalence of multiple scattering, which constitutes a new and unique contrast for ultrasonic imaging. The approach is demonstrated for a controllable phantom system and for in vivo imaging of the human abdomen. More generally, this matrix approach opens an original and powerful route for quantitative imaging in wave physics.
Distortion matrix concept for deep optical imaging in scattering media Badon, A., V. Barolle, K. Irsch, A. Claude Boccara, M. Fink, and A. Aubry Science Advances 6, no. 30 (2020) Résumé: © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC). In optical imaging, light propagation is affected by the inhomogeneities of the medium. Sample-induced aberrations and multiple scattering can strongly degrade the image resolution and contrast. On the basis of a dynamic correction of the incident and/or reflected wavefronts, adaptive optics has been used to compensate for those aberrations. However, it only applies to spatially invariant aberrations or to thin aberrating layers. Here, we propose a global and noninvasive approach based on the distortion matrix concept. This matrix basically connects any focusing point of the image with the distorted part of its wavefront in reflection. A singular value decomposition of the distortion matrix allows to correct for high-order aberrations and forward multiple scattering over multiple isoplanatic modes. Proof-of-concept experiments are performed through biological tissues including a turbid cornea. We demonstrate a Strehl ratio enhancement up to 2500 and recover a diffraction-limited resolution until a depth of 10 scattering mean free paths.
Dynamic full-field optical coherence tomography: 3D live-imaging of retinal organoids Scholler, J., K. Groux, O. Goureau, J. A. Sahel, M. Fink, S. Reichman, C. Boccara, and K. Grieve Light: Science and Applications 9, no. 1 (2020) Résumé: © 2020, The Author(s). Optical coherence tomography offers astounding opportunities to image the complex structure of living tissue but lacks functional information. We present dynamic full-field optical coherence tomography as a technique to noninvasively image living human induced pluripotent stem cell-derived retinal organoids. Coloured images with an endogenous contrast linked to organelle motility are generated, with submicrometre spatial resolution and millisecond temporal resolution, creating a way to identify specific cell types in living tissue via their function.
Functional ultrasound imaging of deep visual cortex in awake nonhuman primates Blaize, K., F. Arcizet, M. Gesnik, H. Ahnine, U. Ferrari, T. Deffieux, P. Pouget, F. Chavane, M. Fink, J. A. Sahel, J. A. Sahel, J. A. Sahel, M. Tanter, and S. Picaud Proceedings of the National Academy of Sciences of the United States of America 117, no. 25, 14453-14463 (2020) Résumé: © 2020 National Academy of Sciences. All rights reserved. Deep regions of the brain are not easily accessible to investigation at the mesoscale level in awake animals or humans. We have recently developed a functional ultrasound (fUS) technique that enables imaging hemodynamic responses to visual tasks. Using fUS imaging on two awake nonhuman primates performing a passive fixation task, we constructed retinotopic maps at depth in the visual cortex (V1, V2, and V3) in the calcarine and lunate sulci. The maps could be acquired in a single-hour session with relatively few presentations of the stimuli. The spatial resolution of the technology is illustrated by mapping patterns similar to ocular dominance (OD) columns within superficial and deep layers of the primary visual cortex. These acquisitions using fUS suggested that OD selectivity is mostly present in layer IV but with extensions into layers II/III and V. This imaging technology provides a new mesoscale approach to the mapping of brain activity at high spatiotemporal resolution in awake subjects within the whole depth of the cortex. Mots-clés: Brain imaging; Functional ultrasound imaging; Nonhuman primate; Ocular dominance; Visual cortex
Distortion matrix approach for ultrasound imaging of random scattering media Lambert, W., L. A. Cobus, T. Frappart, M. Fink, and A. Aubry Proceedings of the National Academy of Sciences of the United States of America 117, no. 26, 14645-14656 (2020) Résumé: Focusing waves inside inhomogeneous media is a fundamental problem for imaging. Spatial variations of wave velocity can strongly distort propagating wave fronts and degrade image quality. Adaptive focusing can compensate for such aberration but is only effective over a restricted field of view. Here, we introduce a full-field approach to wave imaging based on the concept of the distortion matrix. This operator essentially connects any focal point inside the medium with the distortion that a wave front, emitted from that point, experiences due to heterogeneities. A time-reversal analysis of the distortion matrix enables the estimation of the transmission matrix that links each sensor and image voxel. Phase aberrations can then be unscrambled for any point, providing a full-field image of the medium with diffraction-limited resolution. Importantly, this process is particularly efficient in random scattering media, where traditional approaches such as adaptive focusing fail. Here, we first present an experimental proof of concept on a tissue-mimicking phantom and then, apply the method to in vivo imaging of human soft tissues. While introduced here in the context of acoustics, this approach can also be extended to optical microscopy, radar, or seismic imaging. Mots-clés: acoustic speckle; complex media; sample-induced aberrations; transmission matrix imaging; waves
Real-time non-contact cellular imaging and angiography of human cornea and limbus with common-path full-field/SD OCT Mazlin, V., P. Xiao, J. Scholler, K. Irsch, K. Grieve, M. Fink, and A. C. Boccara Nature Communications 11, no. 1 (2020) Résumé: © 2020, The Author(s). In today’s clinics, a cell-resolution view of the cornea can be achieved only with a confocal microscope (IVCM) in contact with the eye. Here, we present a common-path full-field/spectral-domain OCT microscope (FF/SD OCT), which enables cell-detail imaging of the entire ocular surface in humans (central and peripheral cornea, limbus, sclera, tear film) without contact and in real-time. Real-time performance is achieved through rapid axial eye tracking and simultaneous defocusing correction. Images contain cells and nerves, which can be quantified over a millimetric field-of-view, beyond the capability of IVCM and conventional OCT. In the limbus, palisades of Vogt, vessels, and blood flow can be resolved with high contrast without contrast agent injection. The fast imaging speed of 275 frames/s (0.6 billion pixels/s) allows direct monitoring of blood flow dynamics, enabling creation of high-resolution velocity maps. Tear flow velocity and evaporation time can be measured without fluorescein administration.
Waveform analysis of human retinal and choroidal blood flow with laser Doppler holography Puyo, L., M. Paques, M. Fink, J. A. Sahel, and M. Atlan Biomedical Optics Express 10, no. 10, 4942-4963 (2019) Résumé: © 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement Laser Doppler holography was introduced as a full-field imaging technique to measure blood flow in the retina and choroid with an as yet unrivaled temporal resolution. We here investigate separating the different contributions to the power Doppler signal in order to isolate the flow waveforms of vessels in the posterior pole of the human eye. Distinct flow behaviors are found in retinal arteries and veins with seemingly interrelated waveforms. We demonstrate a full field mapping of the local resistivity index, and the possibility to perform unambiguous identification of retinal arteries and veins on the basis of their systolodiastolic variations. Finally we investigate the arterial flow waveforms in the retina and choroid and find synchronous and similar waveforms, although with a lower pulsatility in choroidal arteries. This work demonstrates the potential held by laser Doppler holography to study ocular hemodynamics in healthy and diseased eyes.
2D airborne ultrasound piezotransducer arrays for corneal imaging Aminot, A., P. Shirkovskiy, C. Dorme, M. Legros, R. Dufait, M. Fink, and R. K. Ing IEEE International Ultrasonics Symposium, IUS 2019-October, 800-802 (2019) Résumé: © 2019 IEEE. Non-contact ultrasound applications are raising more and more interests. However, very few applications have been reported, for now in medical applications. In this work, compact airborne piezotransducers have been designed, built and characterized for a novel medical application: contactless corneal imaging. The emission transducer is cylindrical with a 5.5 mm diameter and the reception transducer is a 2D array of 4x16 elements. A specific emission-reception electronic is also designed for these transducers to drive their high electric impedances that are larger than kiloOhms. The measured parameters - directivity, sensitivity and frequency bandwidth - of both transducers respond well to the needs of corneal imaging application. Mots-clés: 2D airborne transducer array; airborne ultrasound transducer; Non-contact ultrasonic imaging
How a moving passive observer can perceive its environment ? The Unruh effect revisited Fink, M., and J. Garnier Wave Motion 93 (2020) Résumé: © 2019 Elsevier B.V. We consider a point-like observer that moves in a medium illuminated by noise sources with Lorentz-invariant spectrum. We show that the autocorrelation function of the signal recorded by the observer allows it to perceive its environment. More precisely, we consider an observer with constant acceleration (along a Rindler trajectory) and we exploit the recent work on the emergence of the Green's function from the cross correlation of signals transmitted by noise sources. First we recover the result that the signal recorded by the observer has a constant Wigner transform, i.e. a constant local spectrum, when the medium is homogeneous (this is the classical analogue of the Unruh effect). We complete that result by showing that the Rindler trajectory is the only straight-line trajectory that satisfies this property. We also show that, in the presence of an obstacle in the form of an infinite perfect mirror, the Wigner transform is perturbed when the observer comes into the neighborhood of the obstacle. The perturbation makes it possible for the observer to determine its position relative to the obstacle once the entire trajectory has been traversed. Mots-clés: Correlation-based imaging; Moving sensors; Noise sources; Passive imaging; Rindler trajectory; Unruh effect
Smart radio environments empowered by reconfigurable AI meta-surfaces: an idea whose time has come Renzo, M. D., M. Debbah, D. T. Phan-Huy, A. Zappone, M. S. Alouini, C. Yuen, V. Sciancalepore, G. C. Alexandropoulos, J. Hoydis, H. Gacanin, J. d. Rosny, A. Bounceur, G. Lerosey, and M. Fink Eurasip Journal on Wireless Communications and Networking 2019, no. 1 (2019) Résumé: © 2019, The Author(s). Future wireless networks are expected to constitute a distributed intelligent wireless communications, sensing, and computing platform, which will have the challenging requirement of interconnecting the physical and digital worlds in a seamless and sustainable manner. Currently, two main factors prevent wireless network operators from building such networks: (1) the lack of control of the wireless environment, whose impact on the radio waves cannot be customized, and (2) the current operation of wireless radios, which consume a lot of power because new signals are generated whenever data has to be transmitted. In this paper, we challenge the usual “more data needs more power and emission of radio waves” status quo, and motivate that future wireless networks necessitate a smart radio environment: a transformative wireless concept, where the environmental objects are coated with artificial thin films of electromagnetic and reconfigurable material (that are referred to as reconfigurable intelligent meta-surfaces), which are capable of sensing the environment and of applying customized transformations to the radio waves. Smart radio environments have the potential to provide future wireless networks with uninterrupted wireless connectivity, and with the capability of transmitting data without generating new signals but recycling existing radio waves. We will discuss, in particular, two major types of reconfigurable intelligent meta-surfaces applied to wireless networks. The first type of meta-surfaces will be embedded into, e.g., walls, and will be directly controlled by the wireless network operators via a software controller in order to shape the radio waves for, e.g., improving the network coverage. The second type of meta-surfaces will be embedded into objects, e.g., smart t-shirts with sensors for health monitoring, and will backscatter the radio waves generated by cellular base stations in order to report their sensed data to mobile phones. These functionalities will enable wireless network operators to offer new services without the emission of additional radio waves, but by recycling those already existing for other purposes. This paper overviews the current research efforts on smart radio environments, the enabling technologies to realize them in practice, the need of new communication-theoretic models for their analysis and design, and the long-term and open research issues to be solved towards their massive deployment. In a nutshell, this paper is focused on discussing how the availability of reconfigurable intelligent meta-surfaces will allow wireless network operators to redesign common and well-known network communication paradigms. Mots-clés: 6G wireless; Environmental AI; Reconfigurable intelligent meta-surfaces; Smart radio environments
Phase-conjugate mirror for water waves driven by the Faraday instability Bacot, V., G. Durey, A. Eddi, M. Fink, and E. Fort Proceedings of the National Academy of Sciences of the United States of America 116, no. 18, 8809-8814 (2019) Résumé: The Faraday instability appears on liquid baths submitted to vertical oscillations above a critical value. The pattern of standing ripples at half the vibrating frequency that results from this parametric forcing is usually shaped by the boundary conditions imposed by the enclosing receptacle. Here, we show that the time modulation of the medium involved in the Faraday instability can act as a phase-conjugate mirror--a fact which is hidden in the extensively studied case of the boundary-driven regime. We first demonstrate the complete analogy with the equations governing its optical counterpart. We then use water baths combining shallow and deep areas of arbitrary shapes to spatially localize the Faraday instability. We give experimental evidence of the ability of the Faraday instability to generate counterpropagating phase-conjugated waves for any propagating signal wave. The canonical geometries of a point and plane source are implemented. We also verify that Faraday-based phase-conjugate mirrors hold the genuine property of being shape independent. These results show that a periodic modulation of the effective gravity can perform time-reversal operations on monochromatic propagating water waves, with a remarkable efficiency compared with wave manipulation in other fields of physics. Mots-clés: Faraday instability; phase-conjugate mirror; water wave; wave control
Drastic slowdown of the Rayleigh-like wave in unjammed granular suspensions Brum, J., J. L. Gennisson, M. Fink, A. Tourin, and X. Jia Physical Review E 99, no. 4 (2019) Résumé: © 2019 American Physical Society. We present an experimental investigation of Rayleigh-like wave propagation along the surface of a dense granular suspension. Using an ultrafast ultrasound scanner, we monitor the softening of the shear modulus via the Rayleigh-like wave velocity slowdown in the optically opaque medium as the driving amplitude increases. For such nonlinear behavior two regimes are found when increasingthe driving amplitude progressively: First, we observe a significant shear modulus weakening due to the microslip on the contact level without macroscopic rearrangements of grains. Second, there is a clear macroscopic plastic rearrangement accompanied by a modulus decrease up to 88%. A friction model is proposed to describe the interplay between nonlinear elasticity and plasticity, which highlights the crucial effect of contact slipping before contact breaking or loss. Investigation of this nonlinear Rayleigh-like wave may bridge the gap between two disjoint approaches for describing the dynamics near unjamming: linear elastic soft modes and nonlinear collisional shock.
Left-handed band in an electromagnetic metamaterial induced by sub-wavelength multiple scattering Yves, S., T. Berthelot, M. Fink, G. Lerosey, and F. Lemoult Applied Physics Letters 114, no. 11 (2019) Résumé: © 2019 Author(s). Due to the deep sub-wavelength unit cell in metamaterials, the quasi-static approximation is usually employed to describe the propagation. By making pairs of resonators, we highlight that multiple scattering also occurs at this scale and results in the existence of a dipolar resonance, which leads to a negative index of refraction when we consider several resonators. We experimentally verify the possibility of obtaining a negative index of refraction in periodic metamaterials in two different ways and eventually demonstrate the subwavelength recovery of several point sources in both cases.
In vivo high-resolution human retinal imaging with wavefront-correctionless full-field OCT Xiao, P., V. Mazlin, K. Grieve, J. Sahel, M. Fink, and A. C. Boccara Optica 5, 409-412 (2018)
In vivo imaging through the entire thickness of human cornea by full-field optical coherence tomography Mazlin, V., P. Xiao, E. Dalimier, K. Grieve, K. Irsch, J. Sahel, M. Fink, and A. C. Boccara Proceedings of SPIE - The International Society for Optical Engineering, 104740S (2018)
In vivo high resolution human corneal imaging using full-field optical coherence tomography Mazlin, V., P. Xiao, E. Dalimier, K. Grieve, K. Irsch, J. Sahel, M. Fink, and A. C. Boccara Biomedical Optics Express 9, 557-568 (2018)
Active Control of the Spoof Plasmon Propagation in Time Varying and Non-reciprocal Metamaterial Ourir, A., and M. Fink Scientific Reports 9, no. 1 (2019) Résumé: © 2019, The Author(s). We present an efficient concept based on time varying and non reciprocal metamaterials to achieve an active control of the spoof plasmon (SP) propagation at sub-wavelength scale. An experimental demonstration of non-reciprocal guiding device based on split ring resonator is proposed as an application of this concept in the microwave regime. We show that this device is able to blue-shift the propagated SP waves and to achieve an active steering of these SPs at sub-wavelength scale by controlling the modulation frequency of the time varying metamaterial. This approach could be extended plainly to infrared and optical regimes by considering suitable technologies.
Choroidal vasculature imaging with laser doppler holography Puyo, L., M. Paques, M. Fink, J. A. Sahel, and M. Atlan Biomedical Optics Express 10, no. 2 (2019) Résumé: © 2019 Optical Society of America. The choroid is a highly vascularized tissue supplying the retinal pigment epithelium and photoreceptors. Its implication in retinal diseases is gaining increasing interest. However, investigating the anatomy and flow of the choroid remains challenging. Here we show that laser Doppler holography provides high-contrast imaging of choroidal vessels in humans, with a spatial resolution comparable to state-of-the-art indocyanine green angiography and optical coherence tomography. Additionally, laser Doppler holography contributes to sort out choroidal arteries and veins by using a power Doppler spectral analysis. We thus demonstrate the potential of laser Doppler holography to improve our understanding of the anatomy and flow of the choroidal vascular network.
Probing dynamic processes in the eye at multiple spatial and temporal scales with multimodal full field OCT Scholler, J., V. Mazlin, O. Thouvenin, K. Groux, P. Xiao, J. A. Sahel, M. Fink, C. Boccara, and K. Grieve Biomedical Optics Express 10, no. 2, 731-746 (2019) Résumé: © 2019 Optical Society of America. We describe recent technological progress in multimodal en face full-field optical coherence tomography that has allowed detection of slow and fast dynamic processes in the eye. We show that by combining static, dynamic and fluorescence contrasts we can achieve label-free high-resolution imaging of the retina and anterior eye with temporal resolution from milliseconds to several hours, allowing us to probe biological activity at subcellular scales inside 3D bulk tissue. Our setups combine high lateral resolution over a large field of view with acquisition at several hundreds of frames per second which make it a promising tool for clinical applications and biomedical studies. Its contactless and non-destructive nature is shown to be effective for both following in vitro sample evolution over long periods of time and for imaging of the human eye in vivo.
Controlling light in complex media beyond the acoustic diffraction-limit using the acousto-optic transmission matrix Katz, O., F. Ramaz, S. Gigan, and M. Fink Nature Communications 10, no. 1 (2019) Résumé: © 2019, The Author(s). Studying the internal structure of complex samples with light is an important task but a difficult challenge due to light scattering. While the complex optical distortions induced by scattering can be effectively undone if the medium’s scattering-matrix is known, this matrix generally cannot be retrieved without the presence of an invasive detector or guide-star at the target points of interest. To overcome this limitation, the current state-of-the-art approaches utilize focused ultrasound for generating acousto-optic guide-stars, in a variety of different techniques. Here, we introduce the acousto-optic transmission matrix (AOTM), which is an ultrasonically-encoded, spatially-resolved, optical scattering-matrix. The AOTM provides both a generalized framework to describe any acousto-optic based technique, and a tool for light control and focusing beyond the acoustic diffraction-limit inside complex samples. We experimentally demonstrate complex light control using the AOTM singular vectors, and utilize the AOTM framework to analyze the resolution limitation of acousto-optic guided focusing approaches.
Non-Contact Surface Wave Elastography Using 40 kHz Airborne Ultrasound Surface Motion Camera Aminot, A., P. Shirkovskiy, M. Fink, and R. K. Ing IEEE International Ultrasonics Symposium, IUS 2018-October (2018) Résumé: © 2018 IEEE. The speed of the surface Rayleigh wave, which is related to the viscoelastic properties of the medium, can be measured by non-invasive and non-contact methods. This paper presents a new method for non-contact ultrasound surface wave elastography using airborne ultrasound surface motion camera (AUSMC). To demonstrate and validate the approach the experiments were carried out on different gelatin phantoms of different concentrations (3%, 5%, 8%) and ×12 scaled eye phantom. By studying the dispersion curve of the surface wave speed, shear modulus can be extracted. The study presents the preliminary results that support the capability of the AUSMC system to estimate without contact the shear modulus of semi-infinite media or thin layer over semi-infinite media. Mots-clés: airborne ultrasound vibrometry; Non-contact ultrasonic imaging; surface acoustic wave elastography; surface motion
Optimally diverse communication channels in disordered environments with tuned randomness Del Hougne, P., M. Fink, and G. Lerosey Nature Electronics 2, no. 1, 36-41 (2019) Résumé: © 2019, The Author(s), under exclusive licence to Springer Nature Limited. Multichannel wireless systems have become a standard solution to address our information society’s ever-increasing demand for information transfer. The capacity that such systems can achieve is ultimately limited by the channel diversity in a given propagation medium, and numerous approaches to reduce channel cross-talk by engineering software or hardware details of the signals and antenna arrays have been proposed. Here we show that optimal channel diversity can be achieved by physically shaping the propagation medium itself. Using a reconfigurable metasurface placed inside a random environment, we tune the disorder and impose perfect orthogonality of wireless channels. We report experiments in the microwave domain in which we impose equal weights of the channel matrix eigenvalues for up to 4 × 4 systems, and almost equal weights in larger systems. We also demonstrate enhanced wireless image transmission in an office room in which we augmented the 3 × 3 system’s number of effectively independent channels from two to the optimum of three.
Measuring Dirac Cones in a Subwavelength Metamaterial Yves, S., T. Berthelot, M. Fink, G. Lerosey, and F. Lemoult Physical Review Letters 121, no. 26 (2018) Résumé: © 2018 American Physical Society. The exciting discovery of bidimensional systems in condensed matter physics has triggered the search of their photonic analogues. In this Letter, we describe a general scheme to reproduce some of the systems ruled by a tight-binding Hamiltonian in a locally resonant metamaterial; by specifically controlling the structure and the composition it is possible to engineer the band structure at will. We numerically and experimentally demonstrate this assertion in the microwave domain by reproducing the band structure of graphene, the most famous example of those 2D systems, and by accurately extracting the Dirac cones. This is direct evidence that opting for a crystalline description of those subwavelength scaled systems, as opposed to the usual description in terms of effective parameters, makes them a really convenient tabletop platform to investigate the tantalizing challenges that solid-state physics offer.
Observation of the Talbot effect with water waves Bakman, A., S. Fishman, M. Fink, E. Fort, and S. Wildeman American Journal of Physics 87, no. 1, 38-43 (2019) Résumé: © 2019 American Association of Physics Teachers. When light is incident upon a diffraction grating, images of the grating appear at periodic intervals behind the grating. This phenomenon and the associated self-imaging distance were named after Talbot, who first observed them in the nineteenth century. A century later, this effect held new surprises with the discovery of sub-images at regular fractional distances of the Talbot length. In this paper, we show that water waves enable one to observe the Talbot effect in a classroom experiment. Quantitative measurements, of for example the Talbot distances, can be performed with an easy-to-use digital Schlieren method.
In vivo laser Doppler holography of the human retina Puyo, L., M. Paques, M. Fink, J. A. Sahel, and M. Atlan Biomedical Optics Express 9, no. 9, 4113-4129 (2018) Résumé: © 2018 Optical Society of America. The eye offers a unique opportunity for the non-invasive exploration of cardiovascular diseases. Optical angiography in the retina requires sensitive measurements, which hinders conventional full-field laser Doppler imaging schemes. To overcome this limitation, we used digital holography to perform laser Doppler perfusion imaging of human retina with near-infrared light. Two imaging channels with a slow and a fast CMOS camera were used simultaneously for real-time narrowband measurements, and offline wideband measurements, respectively. The beat frequency spectrum of optical interferograms recorded with the fast (up to 75 kHz ) CMOS camera was analyzed by short-time Fourier transformation. Power Doppler images drawn from the Doppler power spectrum density qualitatively revealed blood flow in retinal vessels over 512 × 512 pixels covering 2.4 × 2.4 mm2on the retina with a temporal resolution down to 1.6 ms. The sensitivity to lateral motion as well as the requirements in terms of sampling frequency are discussed.
Layer potential approach for fast eigenvalue characterization of the Helmholtz equation with mixed boundary conditions Dupré, M., M. Fink, J. Garnier, and G. Lerosey Computational and Applied Mathematics 37, no. 4, 4675-4685 (2018) Résumé: © 2018, SBMAC - Sociedade Brasileira de Matemática Aplicada e Computacional. Our goal is to propose an efficient approach to characterize the eigenvalues and eigenfunctions of the Helmholtz equation with mixed (Dirichlet and Neumann) boundary conditions. Our approach is based on layer potentials. We extend the eigenvalue characterization known for Neumann boundary conditions to the case of mixed boundary conditions. The problem is motivated by the need of such methods for real-time wave-field shaping by electronically tunable surfaces. Mots-clés: Boundary integral equation; Eigenvalue problem; Layer potential
Precise Localization of Multiple Noncooperative Objects in a Disordered Cavity by Wave Front Shaping Del Hougne, P., M. F. Imani, M. Fink, D. R. Smith, and G. Lerosey Physical Review Letters 121, no. 6 (2018) Résumé: © 2018 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the »https://creativecommons.org/licenses/by/4.0/» Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Complicated multipath trajectories of waves in disordered cavities cause object localization to be very challenging with traditional ray-tracing approaches. Yet it is known that information about the object position is encoded in the Green's function. After a calibration step, traditional time-reversal approaches retrieve a source's location from a broadband impulse response measurement. Here, we show that a nonemitting object's scattering contribution to a reverberant medium suffices to localize the object. We demonstrate our finding in the microwave domain. Then, we further simplify the scheme by replacing the temporal degrees of freedom (d.o.f.) of the broadband measurement with spatial d.o.f. obtained from wave front shaping. A simple electronically reconfigurable reflectarray inside the cavity dynamically modulates parts of the cavity boundaries, thereby providing spatial d.o.f. The demonstrated ability to localize multiple noncooperative objects with a single-frequency scheme may have important applications for sensors in smart homes.
Classical analog of the Unruh effect Leonhardt, U., I. Griniasty, S. Wildeman, E. Fort, and M. Fink Physical Review A 98, no. 2 (2018) Résumé: © 2018 American Physical Society. In the Unruh effect an observer with constant acceleration perceives the quantum vacuum as thermal radiation. The Unruh effect has been believed to be a pure quantum phenomenon, but here we show theoretically how the effect arises from the correlation of noise, regardless of whether this noise is quantum or classical. We demonstrate this idea with a simple experiment on water waves where we see the first indications of a Planck spectrum in the correlation energy.
Towards anti-causal Green’s function for three-dimensional sub-diffraction focusing Ma, G., X. Fan, F. Ma, J. De Rosny, P. Sheng, and M. Fink Nature Physics 14, no. 6, 608-612 (2018) Résumé: © 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. In causal physics, the causal Green’s function describes the radiation of a point source. Its counterpart, the anti-causal Green’s function, depicts a spherically converging wave. However, in free space, any converging wave must be followed by a diverging one. Their interference gives rise to the diffraction limit that constrains the smallest possible dimension of a wave’s focal spot in free space, which is half the wavelength. Here, we show with three-dimensional acoustic experiments that we can realize a stand-alone anti-causal Green’s function in a large portion of space up to a subwavelength distance from the focus point by introducing a near-perfect absorber for spherical waves at the focus. We build this subwavelength absorber based on membrane- type acoustic metamaterial, and experimentally demonstrate focusing of spherical waves beyond the diffraction limit.
Shaping reverberating sound fields with an actively tunable metasurface Ma, G., X. Fan, P. Sheng, and M. Fink Proceedings of the National Academy of Sciences of the United States of America 115, no. 26, 6638-6643 (2018) Résumé: © 2018 National Academy of Sciences. All Rights Reserved. A reverberating environment is a common complex medium for airborne sound, with familiar examples such as music halls and lecture theaters. The complexity of reverberating sound fields has hindered their meaningful control. Here, by combining acoustic metasurface and adaptive wavefield shaping, we demonstrate the versatile control of reverberating sound fields in a room. This is achieved through the design and the realization of a binary phase-modulating spatial sound modulator that is based on an actively reconfigurable acoustic metasurface. We demonstrate useful functionalities including the creation of quiet zones and hotspots in a typical reverberating environment. Mots-clés: Acoustics; Metasurface; Reverberation; Wavefront shaping
Airborne ultrasound surface motion camera: Application to seismocardiography Shirkovskiy, P., A. Laurin, N. Jeger-Madiot, D. Chapelle, M. Fink, and R. K. Ing Applied Physics Letters 112, no. 21 (2018) Résumé: © 2018 Author(s). The recent achievements in the accelerometer-based seismocardiography field indicate a strong potential for this technique to address a wide variety of clinical needs. Recordings from different locations on the chest can give a more comprehensive observation and interpretation of wave propagation phenomena than a single-point recording, can validate existing modeling assumptions (such as the representation of the sternum as a single solid body), and provide better identifiability for models using richer recordings. Ultimately, the goal is to advance our physiological understanding of the processes to provide useful data to promote cardiovascular health. Accelerometer-based multichannel system is a contact method and laborious for use in practice, and also even ultralight accelerometers can cause non-negligible loading effects. We propose a contactless ultrasound imaging method to measure thoracic and abdominal surface motions, demonstrating that it is adequate for typical seismocardiogram (SCG) use. The developed method extends non-contact surface-vibrometry to fast 2D mapping by originally combining multi-element airborne ultrasound arrays, a synthetic aperture implementation, and pulsed-waves. Experimental results show the ability of the developed method to obtain 2D seismocardiographic maps of the body surface 30 × 40 cm 2 in dimension, with a temporal sampling rate of several hundred Hz, using ultrasound waves with the central frequency of 40 kHz. Our implementation was validated in-vivo on eight healthy human participants. The shape and position of the zone of maximal absolute acceleration and velocity during the cardiac cycle were also observed. This technology could potentially be used to obtain more complete cardio-vascular information than single-source SCG in and out of clinical environments, due to enhanced identifiability provided by the distributed measurements, and observation of propagation phenomena.
Dynamic Metasurface Aperture as Smart Around-the-Corner Motion Detector Del Hougne, P., M. F. Imani, T. Sleasman, J. N. Gollub, M. Fink, G. Lerosey, and D. R. Smith Scientific Reports 8, no. 1 (2018) Résumé: © 2018 The Author(s). Detecting and analysing motion is a key feature of Smart Homes and the connected sensor vision they embrace. At present, most motion sen sors operate in line-of-sight Doppler shift schemes. Here, we propose an alternative approach suitable for indoor environments, which effectively constitute disordered cavities for radio frequency (RF) waves; we exploit the fundamental sensitivity of modes of such cavities to perturbations, caused here by moving objects. We establish experimentally three key features of our proposed system: (i) ability to capture the temporal variations of motion and discern information such as periodicity ("smart"), (ii) non line-of-sight motion detection, and (iii) single-frequency operation. Moreover, we explain theoretically and demonstrate experimentally that the use of dynamic metasurface apertures can substantially enhance the performance of RF motion detection. Potential applications include accurately detecting human presence and monitoring inhabitants' vital signs.
Towards a quantum time mirror for non-relativistic wave packets Reck, P., C. Gorini, A. Goussev, V. Krueckl, M. Fink, and K. Richter New Journal of Physics 20, no. 3 (2018) Résumé: © 2018 The Author(s). Published by IOP Publishing Ltd on behalf of Deutsche Physikalische Gesellschaft. We propose a method - a quantum time mirror (QTM) - for simulating a partial time-reversal of the free-space motion of a non-relativistic quantum wave packet. The method is based on a short-time spatially homogeneous perturbation to the wave packet dynamics, achieved by adding a nonlinear time-dependent term to the underlying Schrödinger equation. Numerical calculations, supporting our analytical considerations, demonstrate the effectiveness of the proposed QTM for generating a time-reversed echo image of initially localized matter-wave packets in one and two spatial dimensions. We also discuss possible experimental realizations of the proposed QTM. Mots-clés: matter waves; nonlinear Schrdinger equation; quantum scattering; quantum time mirrors; quantum wave packets
Topological spoof plasmon polaritons based on C6-symmetric crystalline metasurfaces Fleury, R., S. Yves, T. Berthelot, M. Fink, F. Lemoult, and G. Lerosey 2017 11th International Congress on Engineered Material Platforms for Novel Wave Phenomena, Metamaterials 2017, 109-111 (2017) Résumé: © 2017 IEEE. We demonstrate topological surface polaritons that propagate on the surface of a two-dimensional (2D) metamaterial made of a subwavelength periodic arrangement of electromagnetic resonators. Such surface modes are obtained at the boundary between 2D domains of distinct topologies, characterized by non-zero spin-Chern invariants, where a spin degree of freedom is induced by relying on six-fold rotational (C6) crystal symmetry combined with time-reversal symmetry. Experiments are conducted in the microwave regime to corroborate the analytical and numerical predictions. Our proposal enables robust subwavelength guiding of electromagnetic waves on a surface along predefined paths.
Shaping Microwave Fields Using Nonlinear Unsolicited Feedback: Application to Enhance Energy Harvesting Del Hougne, P., M. Fink, and G. Lerosey Physical Review Applied 8, no. 6 (2017) Résumé: © 2017 American Physical Society. Wave-front shaping has emerged over the past decade as a powerful tool to control wave propagation through complex media, initially in optics and more recently also in the microwave domain with important applications in telecommunication, imaging, and energy transfer. The crux of implementing wave-front shaping concepts in real life is often its need for (direct) feedback, requiring access to the target to focus on. Here, we present the shaping of a microwave field based on indirect, unsolicited, and blind feedback which may be the pivotal step towards practical implementations. With the example of a radio-frequency harvester in a metallic cavity, we demonstrate tenfold enhancement of the harvested power by wave-front shaping based on nonlinear signals detected at an arbitrary position away from the harvesting device.
Multiple scattering limit in optical microscopy Badon, A., A. C. Boccara, G. Lerosey, M. Fink, and A. Aubry Optics Express 25, no. 23, 28914-28934 (2017) Résumé: © 2017 Optical Society of America. Optical microscopy offers a unique insight of biological structures with a sub-micrometer resolution and a minimum invasiveness. However, the inhomogeneities of the specimen itself can induce multiple scattering of light and optical aberrations which limit the observation to depths close to the surface. To predict quantitatively the penetration depth in microscopy, we theoretically derive the single-to-multiple scattering ratio in reflection. From this key quantity, the multiple scattering limit is deduced for various microscopic imaging techniques such as confocal microscopy, optical coherence tomography and related methods.
Non-contact and through-clothing measurement of the heart rate using ultrasound vibrocardiography Jeger-Madiot, N., J. Gateau, M. Fink, and R. K. Ing Medical Engineering and Physics 50, 96-102 (2017) Résumé: © 2017 IPEM We present a novel non-contact system for monitoring the heart rate on human subjects with clothes. Our approach is based on vibrocardiography, and measures locally skin displacements. Vibrocardiography with a laser Doppler vibrometer already allows monitoring of this vital sign, but can only be used on bare skin and requires an expensive piece of equipment. We propose here to use an airborne pulse-Doppler ultrasound system operating in the 20–60 kHz range, and comprised of an emitter focusing the ultrasound pulses on skin and a microphone recording the reflected waves. Our implementation was validated in vitro and on two healthy human subjects, using simultaneously laser vibrocardiography and electrocardiography as references. Accurate measurements of the heart rate on clothed skin suggest that our non-contact ultrasonic method could be implemented both inside and outside the clinical environment, and therefore benefit both medical and safety applications. Mots-clés: Clothes; Heart rate; Non-contact; Ultrasound vibrometry; Vibrocardiography
Crystalline Soda Can Metamaterial exhibiting Graphene-like Dispersion at subwavelength scale Yves, S., F. Lemoult, M. Fink, and G. Lerosey Scientific Reports 7, no. 1 (2017) Résumé: © 2017 The Author(s). Graphene, a honeycomb lattice of carbon atoms ruled by tight-binding interaction, exhibits extraordinary electronic properties due to the presence of Dirac cones within its band structure. These intriguing singularities have naturally motivated the discovery of their classical analogues. In this work, we present a general and direct procedure to reproduce the peculiar physics of graphene within a very simple acoustic metamaterial: a double lattice of soda cans resonating at two different frequencies. The first triangular sub-lattice generates a bandgap at low frequency, which induces a tight-binding coupling between the resonant defects of the second honeycomb one, hence allowing us to obtain a graphene-like band structure. We prove the relevance of this approach by showing that both numerical and experimental dispersion relations exhibit the requested Dirac cone. We also demonstrate the straightforward monitoring of the coupling strength within the crystal of resonant defects. This work shows that crystalline metamaterials are very promising candidates to investigate tantalizing solid-state physics phenomena with classical waves.
Slow waves in locally resonant metamaterials line defect waveguides Kaina, N., A. Causier, Y. Bourlier, M. Fink, T. Berthelot, and G. Lerosey Scientific Reports 7, no. 1 (2017) Résumé: © 2017 The Author(s). Many efforts have been devoted to wave slowing, as it is essential, for instance, in analog signal computing and is one prerequisite for increased wave/matter interactions. Despite the interest of many communities, researches have mostly been conducted in optics, where wavelength-scaled structured composite media are promising candidates for compact slow light components. Yet their structural scale prevents them from being transposed to lower frequencies. Here, we propose to overcome this limitation using the deep sub-wavelength scale of locally resonant metamaterials. We experimentally show, in the microwave regime, that introducing coupled resonant defects in such metamaterials creates sub-wavelength waveguides in which wave propagation exhibit reduced group velocities. We qualitatively explain the mechanism underlying this slow wave propagation and demonstrate how it can be used to tune the velocity, achieving group indices as high as 227. We conclude by highlighting the three beneficial consequences of our line defect slow wave waveguides: (1) the sub-wavelength scale making it a compact platform for low frequencies (2) the large group indices that together with the extreme field confinement enables efficient wave/matter interactions and (3) the fact that, contrarily to other approaches, slow wave propagation does not occur at the expense of drastic bandwidth reductions.
Subwavelength focusing and imaging from the far field using time reversal in subwavelength scaled resonant media Lemoult, F., M. Dupre, M. Fink, and G. Lerosey International Conference on Transparent Optical Networks (2017) Résumé: © 2017 IEEE. In this talk we will show how the use of time dependent and broadband wave fields, in conjunction with media structured at the subwavelength scale and supporting resonant eigenmodes, permits to beat the diffraction limit from the far field for imaging or focusing purposes. Examples will be given in the microwave, the acoustic, and the optical domain.
Effect of microstructural elongation on backscattered field: Intensity measurement and multiple scattering estimation with a linear transducer array Baelde, A., J. Laurent, P. Millien, R. Coulette, W. B. Khalifa, F. Jenson, F. Sun, M. Fink, and C. Prada Ultrasonics 82, 379-389 (2018) Résumé: © 2017 Elsevier B.V. The effect of microstructural elongation on ultrasonic backscattered fields was studied. Two methods for determining the elongation direction of macrozones in titanium alloys, using the anisotropic spatial coherence of the backscattered field, are presented. Both methods use a phased array attached on a rotative holder that records the array response matrix at several angles. Two titanium alloys were investigated: TA6V and Ti17. TA6V exhibited a strong macrozone elongation, whereas Ti17 macrozones were found equiaxial. The first method is based on the measurement of backscattered intensity in function of the probe angle relative to the macrozones elongation direction. An angular dependence of backscattered intensity is observed in presence of elongated scatterers, and their elongation direction is collinear with the probe direction corresponding to a minimal intensity. This variability is linked to both piezoelectric shape and the backscattered field spatial properties. The second method is based on the measurement of the relative proportion of single to multiple scattering in a diffusive media, using a simplified version of the single scattering filter developed in Aubry and Derode (2009). It allows the measurement of the level of multiple scattering: both titanium alloys exhibited strong multiple scattering. The elongation direction was determined as the direction of minimal multiple scattering. Furthermore, these results were confirmed by the measurement of the coherent backscattering cone on both samples.
Manipulating light at subwavelength scale by exploiting defect-guided spoof plasmon modes Ourir, A., A. Maurel, S. Félix, J. F. Mercier, and M. Fink Physical Review B 96, no. 12 (2017) Résumé: © 2017 American Physical Society. We study the defect-guided modes supported by a set of metallic rods structured at the subwavelength scale. Following the idea of photonic crystal waveguide, we show that spoof plasmon surface waves can be manipulated at subwavelength scale. We demonstrate that these waves can propagate without leakage along a row of rods having a different length than the surrounding medium and we provide the corresponding dispersion relation. The principle of this subwavelength colored guide is validated experimentally. This allows us to propose the design of a wavelength demultiplexer whose efficiency is illustrated in the microwave regime.
Topological acoustic polaritons: Robust sound manipulation at the subwavelength scale Yves, S., R. Fleury, F. Lemoult, M. Fink, and G. Lerosey New Journal of Physics 19, no. 7 (2017) Résumé: © 2017 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Topological insulators, a hallmark of condensed matter physics, have recently reached the classical realm of acoustic waves. A remarkable property of time-reversal invariant topological insulators is the presence of unidirectional spin-polarized propagation along their edges, a property that could lead to a wealth of new opportunities in the ability to guide and manipulate sound. Here, we demonstrate and study the possibility to induce topologically non-trivial acoustic states at the deep subwavelength scale, in a structured two-dimensional metamaterial composed of Helmholtz resonators. Radically different from previous designs based on non-resonant sonic crystals, our proposal enables robust sound manipulation on a surface along predefined, subwavelength pathways of arbitrary shapes. Mots-clés: acoustic metamaterials; polaritons; quantum spin Hall effect; topological insulators
Crystalline metamaterials for topological properties at subwavelength scales Yves, S., R. Fleury, T. Berthelot, M. Fink, F. Lemoult, and G. Lerosey Nature Communications 8 (2017) Résumé: The exciting discovery of topological condensed matter systems has lately triggered a search for their photonic analogues, motivated by the possibility of robust backscattering-immune light transport. However, topological photonic phases have so far only been observed in photonic crystals and waveguide arrays, which are inherently physically wavelength scaled, hindering their application in compact subwavelength systems. In this letter, we tackle this problem by patterning the deep subwavelength resonant elements of metamaterials onto specific lattices, and create crystalline metamaterials that can develop complex nonlocal properties due to multiple scattering, despite their very subwavelength spatial scale that usually implies to disregard their structure. These spatially dispersive systems can support subwavelength topological phases, as we demonstrate at microwaves by direct field mapping. Our approach gives a straightforward tabletop platform for the study of photonic topological phases, and allows to envision applications benefiting the compactness of metamaterials and the amazing potential of topological insulators.
From the time-reversal mirror to the instantaneous time mirror Fink, M., and E. Fort European Physical Journal: Special Topics 226, no. 7, 1477-1486 (2017) Résumé: © 2017, The Author(s).Because time and space play a similar role in wave propagation, wave control can be obtained by manipulating spatial boundaries or by manipulating time boundaries. These two dual approaches will be discussed in this paper in the context of the generation of time-reversed waves. The first approach uses the “time-reversal mirror” approach with wave manipulation along a spatial boundary sampled by a finite number of antennas. In the second approach, waves are manipulated from a time boundary and we show that “instantaneous time mirrors”, simultaneously acting in the entire space can also radiate time-reversed waves.
Time reversal of ultrasound in granular media Harazi, M., Y. Yang, M. Fink, A. Tourin, and X. Jia European Physical Journal: Special Topics 226, no. 7, 1487-1497 (2017) Résumé: © 2017, The Author(s).Time reversal (TR) focusing of ultrasound in granular packings is experimentally investigated. Pulsed elastic waves transmitted from a compressional or shear transducer source are measured by a TR mirror, reversed in time and back-propagated. We find that TR of ballistic coherent waves onto the source position is very robust regardless driving amplitude but provides poor spatial resolution. By contrast, the multiply scattered coda waves offer a finer TR focusing at small amplitude by a lens effect. However, at large amplitude, these TR focusing signals decrease significantly due to the vibration-induced rearrangement of the contact networks, leading to the breakdown of TR invariance. Our observations reveal that granular acoustics is in between particle motion and wave propagation in terms of sensitivity to perturbations. These laboratory experiments are supported by numerical simulations of elastic wave propagation in disordered 2D percolation networks of masses and springs, and should be helpful for source location problems in natural processes.
A resolution insensitive to geometrical aberrations by using incoherent illumination and interference imaging Xiao, P., M. Fink, A. H. Gandjbakhche, and A. Claude Boccara European Physical Journal: Special Topics 226, no. 7, 1603-1621 (2017) Résumé: © 2017, The Author(s).This contribution is another opportunity to acknowledge the influence of Roger Maynard on our research work when he pushed one of us (ACB) to explore the field of waves propagating in complex media rather than limiting ourselves to the wavelength scale of thermal waves or near field phenomena. Optical tomography is used for imaging in-depth scattering media such as biological tissues. Optical coherence tomography (OCT) plays an important role in imaging biological samples. Coupling OCT with adaptive optics (AO) in order to correct eye aberrations has led to cellular imaging of the retina. By using our approach called Full-Field OCT (FFOCT) we show that, with spatially incoherent illumination, the width of the point-spread function (PSF) that governs the resolution is not affected by aberrations that induce only a reduction of the signal level. We will describe our approach by starting with the PSF experimental data followed by a simple theoretical analysis, and numerical calculations. Finally full images obtained through or inside scattering and aberrating media will be shown.
Ambient noise correlation-based imaging with moving sensors Fink, M., and J. Garnier Inverse Problems and Imaging 11, no. 3, 477-500 (2017) Résumé: ©2017 American Institute of Mathematical Sciences.Waves can be used to probe and image an unknown medium. Passive imaging uses ambient noise sources to illuminate the medium. This paper considers passive imaging with moving sensors. The motivation is to generate large synthetic apertures, which should result in enhanced resolution. However Doppler effects and lack of reciprocity significantly affect the imaging process. This paper discusses the consequences in terms of resolution and it shows how to design appropriate imaging functions depending on the sensor trajectory and velocity. Mots-clés: Ambient noise sources; Correlation-based imaging; Moving sensors; Passive sensor imaging
Dirac quantum time mirror Reck, P., C. Gorini, A. Goussev, V. Krueckl, M. Fink, and K. Richter Physical Review B - Condensed Matter and Materials Physics 95, no. 16 (2017) Résumé: © 2017 American Physical Society.Both metaphysical and practical considerations related to time inversion have intrigued scientists for generations. Physicists have strived to devise and implement time-inversion protocols, in particular different forms of "time mirrors" for classical waves. Here we propose an instantaneous time mirror for quantum systems, i.e., a controlled time discontinuity generating wave function echoes with high fidelities. This concept exploits coherent particle-hole oscillations in a Dirac spectrum in order to achieve population reversal, and can be implemented in systems such as (real or artificial) graphene.
Imaging the dynamics of cardiac fiber orientation in vivo using 3D Ultrasound Backscatter Tensor Imaging. Papadacci, C., V. Finel, J. Provost, O. Villemain, P. Bruneval, J.-L. Gennisson, M. Tanter, M. Fink, and M. Pernot Scientific reports 7, no. 1, 830 (2017)
Experimental study of multiple scattering in anisotropic titanium alloys Baelde, A., J. Laurent, R. Coulette, W. B. Khalifa, D. Duclos, F. Jenson, M. Fink, and C. Prada AIP Conference Proceedings 1806 (2017) Résumé: © 2017 Author(s).Ultrasonic testing of jet engine titanium alloys is of high importance for the aircraft manufacturing industry. The quality of ultrasonic non-destructive testing is severely impacted by the titanium complex microstructure. These alloys have been extensively studied and single scattering models are now well known and implemented in ultrasonic propagation simulators. In addition, titanium billets and forged parts have been known to exhibit a highly anisotropic microstructure. We studied ultrasonic wave scattering in Ti17 forged disk, through statistical analysis of the backscattered noise generated by the microstructure. More specifically, we focused on the quantification of multiple scattering relative to single scattering in the backscattered wave. To that end, we used the full matrix capture acquisition with a linear transducer array. Two phenomena were used to quantify the proportion of single scattering with respect to multiple scattering. The first is the coherent backscattering effect, used as a binary indicator of multiple scattering. The second is a repurposed version of the multiple scattering filter, recently developed on random rod forest and applied on Inconel alloys. With these methods, significant level of multiple scattering was consistently measured in Ti17 forged disks, showing that ultrasonic testing could be enhanced by filtering the multiple scattering contribution.
Full-field optical coherence tomography as a diagnosis tool: Recent progress with multimodal imaging Thouvenin, O., C. Apelian, A. Nahas, M. Fink, and C. Boccara Applied Sciences (Switzerland) 7, no. 3 (2017) Résumé: © 2017 by the authors.Full-field optical coherence tomography (FF-OCT) is a variant of OCT that is able to register 2D en face views of scattering samples at a given depth. Thanks to its superior resolution, it can quickly reveal information similar to histology without the need to physically section the sample. Sensitivity and specificity levels of diagnosis performed with FF-OCT are 80% to 95% of the equivalent histological diagnosis performances and could therefore benefit from improvement. Therefore, multimodal systems have been designed to increase the diagnostic performance of FF-OCT. In this paper, we will discuss which contrasts can be measured with such multimodal systems in the context of ex vivo biological tissue examination. We will particularly emphasize three multimodal combinations to measure the tissue mechanics, dynamics, and molecular content respectively. Mots-clés: Biomechanics; Cellular metabolism; Dynamics; Fluorescence microscopy; Full-field optical coherence tomography; Mechanical properties; Multimodality
Dynamic multimodal full-field optical coherence tomography and fluorescence structured illumination microscopy Thouvenin, O., M. Fink, and C. Boccara Journal of Biomedical Optics 22, no. 2 (2017) Résumé: © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.We report on the development of a configuration of a multimodal full-field optical coherence tomography (FF-OCT) and fluorescence microscope. Our system can simultaneously acquire FF-OCT and structured illumination microscopy images. Dynamic parallel evolution of tissue microstructures and biochemical environments can be visualized. We use high numerical aperture objectives to optimize the combination of the two modalities. We imaged the propagation of mechanical waves initiated by calcium waves in a heart wall to illustrate the interest of simultaneous recording of mechanical and biochemical information. Mots-clés: full-field optical coherence tomography; multimodality; structured illumination microscopy; tomography
3D functional ultrasound imaging of the cerebral visual system in rodents Gesnik, M., K. Blaize, T. Deffieux, J. L. Gennisson, J. A. Sahel, M. Fink, S. Picaud, and M. Tanter NeuroImage 149, 267-274 (2017) Résumé: © 2017 The Authors3D functional imaging of the whole brain activity during visual task is a challenging task in rodents due to the complex tri-dimensional shape of involved brain regions and the fine spatial and temporal resolutions required to reveal the visual tract. By coupling functional ultrasound (fUS) imaging with a translational motorized stage and an episodic visual stimulation device, we managed to accurately map and to recover the activity of the visual cortices, the Superior Colliculus (SC) and the Lateral Geniculate Nuclei (LGN) in 3D. Cerebral Blood Volume (CBV) responses during visual stimuli were found to be highly correlated with the visual stimulus time profile in visual cortices (r=0.6), SC (r=0.7) and LGN (r=0.7). These responses were found dependent on flickering frequency and contrast, and optimal stimulus parameters for largest CBV increases were obtained. In particular, increasing the flickering frequency higher than 7 Hz revealed a decrease of visual cortices response while the SC response was preserved. Finally, cross-correlation between CBV signals exhibited significant delays (d=0.35 s +/−0.1 s) between blood volume response in SC and visual cortices in response to our visual stimulus. These results emphasize the interest of fUS imaging as a whole brain neuroimaging modality for brain vision studies in rodent models.
Smart optical coherence tomography for ultra-deep imaging through highly scattering media Badon, A., D. Li, G. Lerosey, A. C. Boccara, M. Fink, and A. Aubry Science Advances 2, no. 11 (2016)
Time-reversal of nonlinear waves: Applicability and limitations Ducrozet, G., M. Fink, and A. Chabchoub Physical Review Fluids 1, no. 5 (2016)
Diffuse shear wave imaging: Toward passive elastography using low-frame rate spectral-domain optical coherence tomography Nguyen, T. M., A. Zorgani, M. Lescanne, C. Boccara, M. Fink, and S. Catheline Journal of Biomedical Optics 21, no. 12 (2016) Résumé: © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE).Optical coherence tomography (OCT) can map the stiffness of biological tissue by imaging mechanical perturbations (shear waves) propagating in the tissue. Most shear wave elastography (SWE) techniques rely on active shear sources to generate controlled displacements that are tracked at ultrafast imaging rates. Here, we propose a noise-correlation approach to retrieve stiffness information from the imaging of diffuse displacement fields using low-frame rate spectral-domain OCT. We demonstrated the method on tissue-mimicking phantoms and validated the results by comparison with classic ultrafast SWE. Then we investigated the in vivo feasibility on the eye of an anesthetized rat by applying noise correlation to naturally occurring displacements. The results suggest a great potential for passive elastography based on the detection of natural pulsatile motions using conventional spectral-domain OCT systems. This would facilitate the transfer of OCT-elastography to clinical practice, in particular, in ophthalmology or dermatology. Mots-clés: noise correlation; optical coherence tomography; passive elastography; shear wave imaging; time reversal
3D airborne ultrasound vibrometer for the detection of skin surface heterogeneities Jeger, N., J. Gâteau, M. Fink, and R. K. Ing IEEE International Ultrasonics Symposium, IUS 2016-November (2016) Résumé: © 2016 IEEE.In security applications, several methods are used for detection of hidden objects. Metal detectors and palpation are the most common methods. Non-contact acoustic waves imaging of elastic heterogeneities in superficial body tissues could be an interesting alternative. In this article a 3D airborne ultrasound vibrometer is developed to image with a high framerate the surface motion of the skin surface generated by the propagation of a low frequency surface acoustic wave (SAW). The phase velocity of the SAW is directly related to the elasticity of the superficial layer of the skin surface. The actual framerate of the vibrometer is 556Hz and the sensitivity displacement value is close to the micrometer. Experimental results using a biological tissue mimicking phantom show the ability of the vibrometer to detect a rigid inclusion below the phantom surface. Mots-clés: airborne; elastography; multiwave; non-contact imaging; surface acoustic wave; Ultrasonic imaging; ultrasonic transducers
Spatiotemporal response of rat visual cortex during moving stimuli using Functional Ultrasound (fUS) imaging Gesnik, M., K. Blaize, A. Dizeux, J. A. Sahel, M. Fink, T. Deffieux, J. L. Gennisson, S. Picaud, and M. Tanter IEEE International Ultrasonics Symposium, IUS 2016-November (2016) Résumé: © 2016 IEEE.The spatiotemporal study of the visual system of the rodent is a challenging area that conventional functional imaging modalities, despite fundamental achievements, still struggle to study nowadays. In the other hand Functional Ultrasound (fUS) offers an unprecedented combination of spatiotemporal resolution. By coupling fUS with an adapted visual stimulation device, we mapped the vision-evoked activity in the rodent brain. We then optimized the visual-stimulus toward the spatiotemporal study of the rodent visual pathway using fUS. Mots-clés: angiography; functional ultrasound; rodent brain; vison
Adaptive optics full-field optical coherence tomography Xiao, P., M. Fink, and A. C. Boccara Journal of Biomedical Optics 21, no. 12 (2016) Résumé: © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE).We describe a simple and compact full-field optical coherence tomography (FFOCT) setup coupled to a transmissive liquid crystal spatial light modulator (LCSLM) to induce or correct aberrations. To reduce the system complexity, strict pupil conjugation was abandoned because low-order aberrations are often dominant. We experimentally confirmed a recent theoretical and experimental demonstration that the image resolution was almost insensitive to aberrations that mostly induce a reduction of the signal level. As a consequence, an imagebased algorithm was applied for the optimization process by using the FFOCT image intensity as the metric. Aberration corrections were demonstrated with both an USAF resolution target and biological samples for LCSLM-induced and sample-induced wavefront distortions. Mots-clés: adaptive optics; interference microscopy; optical coherence tomography
Spatio-temporal imaging of light transport in highly scattering media under white light illumination Badon, A., D. Li, G. Lerosey, A. C. Boccara, M. Fink, and A. Aubry Optica 3, no. 11, 1160-1166 (2016)
Time reversal and holography with spacetime transformations Bacot, V., M. Labousse, A. Eddi, M. Fink, and E. Fort Nature Physics 12, no. 10, 972-977 (2016)
Spatio-temporal imaging of light transport in strongly scattering media Badon, A., D. Li, G. Lerosey, C. Boccara, M. Fink, and A. Aubry 2016 URSI International Symposium on Electromagnetic Theory, EMTS 2016, 272-275 (2016) Résumé: © 2016 IEEE.We report on the passive measurement of time-dependent Green's functions in the optical frequency domain with low-coherence interferometry. Inspired by previous studies in acoustics and seismology, we show how the mutual coherence function of a broadband and incoherent wave-field can directly yield the Green's functions between scatterers of a complex medium. Both the ballistic and multiple scattering components of the Green's function are retrieved. This simple and powerful approach directly yields a wealth of information about the medium under investigation. In particular, it allows to investigate locally the growth of the diffusive halo within the scattering medium. Local measurements of transport parameters can thus be performed and allow to image a strongly scattering layer with a unprecedented resolution of a few transport mean free paths. This constitutes a major breakthrough compared to state-of-the-art techniques such as optical diffuse tomography.
Full-field spatially incoherent illumination interferometry: a spatial resolution almost insensitive to aberrations Xiao, P., M. Fink, and A. C. Boccara Optics Letters 41, no. 17, 3920-3923 (2016)
Spatiotemporal Wave Front Shaping in a Microwave Cavity Del Hougne, P., F. Lemoult, M. Fink, and G. Lerosey Physical Review Letters 117, no. 13 (2016)
Soda cans metamaterial: A subwavelength-scaled phononic crystal Lemoult, F., N. Kaina, M. Fink, and G. Lerosey Crystals 6, no. 7 (2016) Résumé: © 2016 by the authors; licensee MDPI, Basel, Switzerland.Photonic or phononic crystals and metamaterials, due to their very different typical spatial scales—wavelength and deep subwavelength—and underlying physical mechanisms—Bragg interferences or local resonances—, are often considered to be very different composite media. As such, while the former are commonly used to manipulate and control waves at the scale of the unit cell, i.e., wavelength, the latter are usually considered for their effective properties. Yet we have shown in the last few years that under some approximations, metamaterials can be used as photonic or phononic crystals, with the great advantage that they are much more compact. In this review, we will concentrate on metamaterials made out of soda cans, that is, Helmholtz resonators of deep subwavelength dimensions. We will first show that their properties can be understood, likewise phononic crystals, as resulting from interferences only, through multiple scattering effects and Fano interferences. Then, we will demonstrate that below the resonance frequency of its unit cell, a soda can metamaterial supports a band of subwavelength varying modes, which can be excited coherently using time reversal, in order to beat the diffraction limit from the far field. Above this frequency, the metamaterial supports a band gap, which we will use to demonstrate cavities and waveguides, very similar to those obtained in phononic crystals, albeit of deep subwavelength dimensions. We will finally show that multiple scattering can be taken advantage of in these metamaterials, by correctly structuring them. This allows to turn a metamaterial with a single negative effective property into a negative index metamaterial, which refracts waves negatively, hence acting as a superlens. Mots-clés: Acoustics; Metamaterial; Multiple scattering; Phononic crystals
High speed optical holography of retinal blood flow Pellizzari, M., M. Simonutti, J. Degardin, J. A. Sahel, M. Fink, M. Paques, and M. Atlan Optics Letters 41, no. 15, 3503-3506 (2016) Résumé: © 2016 Optical Society of America.We performed noninvasive video imaging of retinal blood flow in a pigmented rat by holographic interferometry of near-infrared laser light backscattered by retinal tissue, beating against an off-axis reference beam sampled at a frame rate of 39 kHz with a high throughput camera. Local Doppler contrasts emerged from the envelopes of short-time Fourier transforms and the phase of autocorrelation functions of holograms rendered by Fresnel transformation. This approach permitted imaging of blood flow in large retinal vessels (∼30 microns diameter) over 400 x 400 pixels with a spatial resolution of ∼8 microns and a temporal resolution of ∼6.5 ms.
Using subwavelength diffraction gratings to design open microwave cavities Dupre, M., M. Fink, and G. Lerosey 2013 7th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics, METAMATERIALS 2013, 133-135 (2013) Résumé: Weintroduce an open microwave cavity that has a wall replaced by a sub-wavelength grating. Usually, sub-wavelength gratings show very low transmission. In our experiment, this phenomenon is compensated by the microwave cavity that finally allows all the energy to be transmitted. We study the far field emission of this system and show that coupling the cavity with a sub-wavelength grating gives rise to a zero order emission only at discrete angles and frequencies. We study the relations between angles of emissions and frequencies, the influence of geometric parameters such as the grating fill factor and the behavior of a chaotic cavity. We show that it allows us to make a configurable system that may have many applications in the fields of communications, detection and imaging, and may allow the study of open microwave cavities on a fundamental point of view. © 2013 IEEE.
Time reversal focusing and the diffraction limit Fink, M., J. De Rosny, G. Lerosey, and A. Tourin Proceedings of the International School of Physics "Enrico Fermi" 173, 155-177 (2011) Résumé: Time reversal mirrors refocus an incident-wave field to the position of the original source, regardless of the complexity of the propagation medium. TRMs have now been implemented in a variety of physical scenarios from GHz Microwaves to MHz Ultrasonics and to hundreds of Hz in ocean acoustics. Common to this broad range of scales is a remarkable robustness exemplified by observations at all scales that the more complex the medium (random or chaotic), the sharper the focus. A TRM acts as an antenna that uses complex environments to appear wider than it is, resulting, for a broad-band pulse, in a refocusing quality that does not depend on the TRM aperture. Moreover, when the complex environment is located in the near field of the source, time reversal focusing opens completely new approaches to super-resolution. We will shown that, for a broad-band source located inside a random metamaterial, a TRM located in the far field radiates a time-reversed wave that interacts with the random medium to regenerate not only the propagating but also the evanescent waves required to refocus below the diffraction limit. © 2011 by Società Italiana di Fisica.
MultiWave imaging Fink, M., and M. Tanter Proceedings of the International School of Physics "Enrico Fermi" 173, 133-153 (2011) Résumé: Interactions between waves can be turned into profit to break diffraction limits and invent new kinds of medical images. It consists in productively combining two very different waves -one to provide contrast, another to provide spatial resolution- in order to build a new kind of image. Contrary to multimodality medical imaging that remains the superposition of two different images limited by their respective contrast/resolution couples, MultiWave imaging overcomes this limitation by providing a unique image of the most interesting contrast with the most interesting resolution. MultiWave imaging can benefit from three different potential interactions among waves that will be described in this paper. © 2011 by Società Italiana di Fisica.
Pulsatile microvascular blood flow imaging by short-time Fourier transform analysis of ultrafast laser holographic interferometry Puyo, L., I. Ferezou, A. Rancillac, M. Simonutti, M. Paques, J. A. Sahel, M. Fink, and M. Atlan BMEiCON 2015 - 8th Biomedical Engineering International Conference (2016) Résumé: © 2015 IEEE. We report on wide-field imaging of pulsatile microvascular blood flow in the exposed cerebral cortex of a mouse by holographic interferometry. We recorded interferograms of laser light backscattered by the tissue, beating against an off-axis reference beam with a 50 kHz framerate camera. Videos of local Doppler contrasts were rendered numerically by Fresnel transformation and short-time Fourier transform analysis. This approach enabled instantaneous imaging of pulsatile blood flow contrasts in superficial blood vessels over 256 x 256 pixels with a spatial resolution of 10 microns and a temporal resolution of 20 ms. Mots-clés: blood flow imaging; holography; laser Doppler
Exploiting spatiotemporal degrees of freedom for far-field subwavelength focusing using time reversal in fractals Dupré, M., F. Lemoult, M. Fink, and G. Lerosey Physical Review B - Condensed Matter and Materials Physics 93, no. 18 (2016) Résumé: © 2016 American Physical Society. Materials which possess a high local density of states varying at a subwavelength scale theoretically permit the focusing of waves onto focal spots much smaller than the free space wavelength. To do so, metamaterials - manmade composite media exhibiting properties not available in nature - are usually considered. However, this approach is limited to narrow bandwidths due to their resonant nature. Here, we prove that it is possible to use a fractal resonator alongside time reversal to focus microwaves onto λ/15 subwavelength focal spots from the far field, on extremely wide bandwidths. We first numerically prove that this approach can be realized using a multiple-channel time reversal mirror that utilizes all the degrees of freedom offered by the fractal resonator. Then, we experimentally demonstrate that this approach can be drastically simplified by coupling the fractal resonator to a complex medium, here a cavity, that efficiently converts its spatial degrees of freedom into temporal ones. This makes it possible to achieve deep subwavelength focusing of microwave radiation by time reversing a single channel. Our method can be generalized to other systems coupling complex media and fractal resonators.
From Loschmidt daemons to time-reversed waves Fink, M. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 374, no. 2069 (2016) Résumé: © 2016 The Author(s) Published by the Royal Society. All rights reserved. Time-reversal invariance can be exploited in wave physics to control wave propagation in complex media. Because time and space play a similar role in wave propagation, time-reversed waves can be obtained by manipulating spatial boundaries or by manipulating time boundaries. The two dual approaches will be discussed in this paper. The first approach uses -time-reversal mirrors- with a wave manipulation along a spatial boundary sampled by a finite number of antennas. Related to this method, the role of the spatiooral degrees of freedom of the wavefield will be emphasized. In a second approach, waves are manipulated from a time boundary and we show that -instantaneous timemirrors-, mimicking the Loschmidt point of view, simultaneously acting in the entire space at once can also radiate time-reversed waves. Mots-clés: Green-s functions; Loschmidt daemons; Subwavelength focusing; Time-reversed waves; Wave propagation in complex media
Negative refractive index and acoustic superlens from multiple scattering in single negative metamaterials. Kaina, N., F. Lemoult, M. Fink, and G. Lerosey Nature 525, no. 7567, 77-81 (2015)
Carotid stiffness change over the cardiac cycle by ultrafast ultrasound imaging in healthy volunteers and vascular Ehlers-Danlos syndrome. Mirault, T., M. Pernot, M. Frank, M. Couade, R. Niarra, M. Azizi, J. Emmerich, X. Jeunemaitre, M. Fink, M. Tanter, and E. Messas Journal of hypertension 33, no. 9, 1890-6 (2015)
Wave-Field Shaping in Cavities: Waves Trapped in a Box with Controllable Boundaries Dupré, M., P. Del Hougne, M. Fink, F. Lemoult, and G. Lerosey Physical Review Letters 115, 017701 (2015)
Transmission glass-like aberrations correction for full-field OCT Imaging Xiao, P., M. Fink, and A. C. Boccara Adaptive Optics: Analysis, Methods and Systems, AO 2015, 289 (2015) Résumé: We show that a Full-Field OCT imaging system could be directly coupled to a compact transmissive liquid crystal spatial light modulator to induce or correct aberrations. The metric is based on the FFOCT image quality. © 2015 OSA.
Optical detection and imaging in complex media: How the memory effect can help overcome multiple scattering Badon, A., D. Li, G. Lerosey, A. C. Boccara, M. Fink, and A. Aubry CLEO: QELS - Fundamental Science, CLEO_QELS 2015, 1551p (2015) Résumé: We report on imaging in random scattering media. Our approach is based on the measurement of a reflection matrix between a spatial light modulator and a camera. We take advantage of the memory effect to filter the multiple scattering noise and improve the detection and imaging of objects embedded in scattering media. © 2014 Optical Society of America.
Overcoming multiple scattering for detection and imaging in strongly scattering media Badon, A., D. Li, G. Lerosey, C. Boccara, M. Fink, and A. Aubry Adaptive Optics: Analysis, Methods and Systems, AO 2015, 289 (2015) Résumé: We report on imaging through thick scattering media based on a matrix approach of wave propagation. We show how to overcome multiple scattering and demonstrate imaging of targets beyond several transport mean free paths. © 2015 OSA.
Retrieving time-dependent Green's functions in optics with low-coherence interferometry Badon, A., G. Lerosey, A. C. Boccara, M. Fink, and A. Aubry CLEO: QELS - Fundamental Science, CLEO_QELS 2015, 1551p (2015) Résumé: We report on the passive measurement of time-dependent Green's functions in optics with low-coherence interferometry. Inspired by previous studies in acoustics and seismology, we show how the correlations of a broadband and incoherent wave-field can directly yield the Green's functions between scatterers of a complex medium. © 2014 Optical Society of America.
Subwavelength focusing in bubbly media using broadband time reversal Lanoy, M., R. Pierrat, F. Lemoult, M. Fink, V. Leroy, and A. Tourin Physical Review B 91, no. 22 (2015)
Scanning-free imaging through a single fiber by random spatio-spectral encoding Kolenderska, S. M., O. Katz, M. Fink, and S. Gigan Optics Letters 40, no. 4, 534-537 (2015) Résumé: © 2015 Optical Society of America. We present an approach for 2D imaging through a single fiber without the need for scanners. A random scattering medium placed next to the distal end of the fiber is used to encode the collected light from every imaged pixel with a different random spectral signature. We demonstrate imaging of externally illuminated 2D objects from a single measured spectrum at the fiber's proximal end. The technique is insensitive to fiber bending, an advantage for endoscopic applications.
Super-resolution in time-reversal focusing on a moving source Garnier, J., and M. Fink Wave Motion 53, 80-93 (2015) Résumé: © 2014 Elsevier B.V. This paper presents a detailed analysis of time-reversal experiments involving a moving point source that emits a pulse. Different configurations are addressed with full-aperture or partial-aperture time-reversal mirrors and with subsonic or supersonic sources. Doppler effects and lack of source-receiver reciprocity significantly affect the time-reversal refocusing when the velocity of the source becomes comparable as or larger than the speed of propagation. The main result is that refocusing can be enhanced when the velocity of the source becomes close to the speed of propagation compared to the classical diffraction-limited refocusing properties when the source does not move, and this super-resolution effect can be quantified by simple and explicit formulas. Mots-clés: Moving sources; Super-resolution; Time reversal
Image transmission through a scattering medium: Inverse problem and sparsity-based imaging Gigan, S., S. M. Popoff, A. Liutkus, D. Martina, O. Katz, G. Chardon, R. Carminati, G. Lerosey, M. A. Fink., A. C. Boccara, I. Carron, and L. Daudet 2014 13th Workshop on Information Optics, WIO 2014 (2014) Résumé: © 2014 IEEE. We demonstrate how to measure accurately the transmission matrix of a complex medium. With this information, we show how to focus light, recover an image, and even perform efficient reconstruction of a sparse object.
High-contrast ultrafast imaging of the heart Papadacci, C., M. Pernot, M. Couade, M. A. Fink., and M. Tanter IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 61, no. 2, 288-301 (2014) Résumé: Noninvasive ultrafast imaging of intrinsic waves such as electromechanical waves or remotely induced shear waves in elastography imaging techniques for human cardiac applications remains challenging. In this paper, we propose ultrafast imaging of the heart with adapted sector size by coherently compounding diverging waves emitted from a standard transthoracic cardiac phased-array probe. As in ultrafast imaging with plane wave coherent compounding, diverging waves can be summed coherently to obtain high-quality images of the entire heart at high frame rate in a full field of view. To image the propagation of shear waves with a large SNR, the field of view can be adapted by changing the angular aperture of the transmitted wave. Backscattered echoes from successive circular wave acquisitions are coherently summed at every location in the image to improve the image quality while maintaining very high frame rates. The transmitted diverging waves, angular apertures, and subaperture sizes were tested in simulation, and ultrafast coherent compounding was implemented in a commercial scanner. The improvement of the imaging quality was quantified in phantoms and in one human heart, in vivo. Imaging shear wave propagation at 2500 frames/s using 5 diverging waves provided a large increase of the SNR of the tissue velocity estimates while maintaining a high frame rate. Finally, ultrafast imaging with 1 to 5 diverging waves was used to image the human heart at a frame rate of 4500 to 900 frames/s over an entire cardiac cycle. Spatial coherent compounding provided a strong improvement of the imaging quality, even with a small number of transmitted diverging waves and a high frame rate, which allows imaging of the propagation of electromechanical and shear waves with good image quality. © 2014 IEEE.
Retrieving time-dependent green's functions in optics with low-coherence interferometry Badon, A., G. Lerosey, A. C. Boccara, M. Fink, and A. Aubry Physical Review Letters 114, no. 2 (2015) Résumé: © 2015 American Physical Society. We report on the passive measurement of time-dependent Green's functions in the optical frequency domain with low-coherence interferometry. Inspired by previous studies in acoustics and seismology, we show how the correlations of a broadband and incoherent wave field can directly yield the Green's functions between scatterers of a complex medium. Both the ballistic and multiple scattering components of the Green's function are retrieved. This approach opens important perspectives for optical imaging and characterization in complex scattering media.
Non-invasive single-shot imaging through scattering layers and around corners via speckle correlations Katz, O., P. Heidmann, M. Fink, and S. Gigan Nature Photonics 8, no. 10 (2014)
Shaping complex microwave fields in reverberating media with binary tunable metasurfaces. Kaina, N., M. Dupre, G. Lerosey, and M. Fink Scientific reports 4, 6693 (2014)
3D ultrafast ultrasound imaging in vivo Provost, J., C. Papadacci, J. E. Arango, M. Imbault, M. Fink, J.-L. Gennisson, M. Tanter, and M. Pernot Physics In Medicine And Biology 59, no. 19, L1-L13 (2014) Mots-clés: ultrasound imaging; ultrafast imaging; 3D ultrasound imaging; volumetric imaging; blood flow; tissue Doppler; cardiac imaging
Cancellation of Doppler Intrinsic Spectral Broadening Using Ultrafast Doppler Imaging Osmanski, B.-F., J. Bercoff, G. Montaldo, T. Loupas, M. Fink, and M. Tanter Ieee Transactions On Ultrasonics Ferroelectrics And Frequency Control 61, no. 8, 1396-1408 (2014)
Ultrasound Backscatter Tensor Imaging (BTI): Analysis of the Spatial Coherence of Ultrasonic Speckle in Anisotropic Soft Tissues Papadacci, C., M. Tanter, M. Pernot, and M. Fink Ieee Transactions On Ultrasonics Ferroelectrics And Frequency Control 61, no. 6, 986-996 (2014)
Towards Backscatter Tensor Imaging (BTI): Analysis of the spatial coherence of ultrasonic speckle in anisotropic soft tissues Papadacci, C., M. Pernot, M. Tanter, and M. Fink IEEE International Ultrasonics Symposium, 1200-1203 (2013)
Shear wave dispersion for fibrosis, steatosis and activity staging Deffieux, T., J.-L. Gennisson, M. Fink, M. Tanter, L. B. Ousquet, D. Amroun, M. Corouge, V. Mallet, and S. Pol IEEE International Ultrasonics Symposium, 523-526 (2013) Mots-clés: component; elastography; liver; fibrosis; steatosis; activity; biopsies; blood tests; shear wave; dispersion; shear wave spectropscopy
In vivo out-of-plane Doppler imaging based on ultrafast plane wave imaging Osmanski, B.-F., G. Montaldo, M. Fink, and M. Tanter IEEE International Ultrasonics Symposium, 76-79 (2013) Mots-clés: Ultrafast imaging; Ultrafast Doppler; Blood flow; Flow vector
In vivo transthoracic ultrafast Doppler imaging of left intraventricular blood flow pattern Osmanski, B.-F., M. Pernot, M. Fink, and M. Tanter IEEE International Ultrasonics Symposium, 1741-1744 (2013) Mots-clés: Ultrafast imaging; Ultrafast Doppler; Heart; Blood flow; Left ventricle
Use of shear wave elastography for monitoring enzymatic milk coagulation Budelli, E., M. Bernal, P. Lema, M. Fink, C. Negreira, M. Tanter, and J. L. Gennisson Journal Of Food Engineering 136, 73-79 (2014) Mots-clés: Shear wave elastography; Milk coagulation; Rheological properties; Ultrafast ultrasound imaging
Time-Reversal Generation of Rogue Waves Chabchoub, A., and M. Fink Physical Review Letters 112, no. 12 (2014)
Using Subwavelength Diffraction Gratings to Design Open Electromagnetic Cavities Dupre, M., M. Fink, and G. Lerosey Physical Review Letters 112, no. 4 (2014)
Subwavelength far-field imaging at visible and ultraviolet wavelengths using broadband surface plasmon waves Ourir, A., and M. Fink Physical Review B 89, no. 11 (2014)
High-Contrast Ultrafast Imaging of the Heart Papadacci, C., M. Pernot, M. Couade, M. Fink, and M. Tanter Ieee Transactions On Ultrasonics Ferroelectrics And Frequency Control 61, no. 2, 288-301 (2014)
From supersonic shear wave imaging to full-field optical coherence shear wave elastography Nahas, A., M. Tanter, Thu-Mai Nguyen, J.-M. Chassot, M. Fink, and A. C. Boccara Journal Of Biomedical Optics 18, no. 12 (2013) Mots-clés: optical coherence tomography; elastography; shear wave imaging; cancer diagnosis
Increasing the modal density in plates for mono-element focusing in air Etaix, N., J. Dubois, M. Fink, and R.-K. Ing Journal Of The Acoustical Society Of America 134, no. 2, 1049-1054 (2013)
A review of the medical applications of shear wave elastography. Tanter, M., M. Pernot, J. L. Gennisson, and M. Fink The Journal of the Acoustical Society of America 134, no. 5, 4009 (2013)
Non-invasive ultrasonic surgery of the brain in non-human primates Marquet, F., A.-L. Boch, M. Pernot, G. Montaldo, D. Seilhean, M. Fink, M. Tanter, and J.-F. Aubry Journal Of The Acoustical Society Of America 134, no. 2, 1632-1639 (2013)
Shear Wave Imaging of the heart using a cardiac phased array with coherent spatial compound Papadacci, C., M. Pernot, M. Couade, M. Fink, and M. Tanter IEEE International Ultrasonics Symposium, 2023-2026 (2012)
Ultrafast Imaging in Biomedical Ultrasound Tanter, M., and M. Fink Ieee Transactions On Ultrasonics Ferroelectrics And Frequency Control 61, no. 1, 102-119 (2014)
Ultrafast imaging in biomedical ultrasound Tanter, M., and M. Fink 61, 102-119 (2014) Résumé: Although the use of ultrasonic plane-wave transmissions rather than line-per-line focused beam transmissions has been long studied in research, clinical application of this technology was only recently made possible through developments in graphical processing unit (GPU)-based platforms. Far beyond a technological breakthrough, the use of plane or diverging wave transmissions enables attainment of ultrafast frame rates (typically faster than 1000 frames per second) over a large field of view. This concept has also inspired the emergence of completely novel imaging modes which are valuable for ultrasound-based screening, diagnosis, and therapeutic monitoring. In this review article, we present the basic principles and implementation of ultrafast imaging. In particular, present and future applications of ultrafast imaging in biomedical ultrasound are illustrated and discussed.
Sono-activated ultrasound localization microscopy Desailly, Y., O. Couture, M. Fink, and M. Tanter Applied Physics Letters 103, no. 17 (2013) Résumé: Scanned at very high ultrasound frame rates, injectable microbubbles can be activated sequentially as isolated punctual sources of acoustic echoes. These signals can thus be localized far beyond the diffraction limit. The resolution improvement granted by Sono-Activated Ultrasound Localization Microscopy (SAULM) was demonstrated within microfluidic channels 20 times smaller than the imaging wavelength (λ = 870 μm). The width of the channels mapped with SAULM was 13 times smaller than as they appeared under conventional ultrasound imaging. Two channels separated by λ/4.5 could be distinguished. Implementing SAULM in-vivo could lead to a complete reconstruction of the vascular tree down to the smallest capillaries at several centimeter depth. © 2013 AIP Publishing LLC.
Ultrafast plane wave imaging: Doppler frequency distribution Osmanski, B.-F., G. Montaldo, J. Bercoff, T. Loupas, M. Fink, and M. Tanter 2012 IEEE International Ultrasonics Symposium, 1580-1583 (2012) Mots-clés: Bandwidth; Carotid arteries; Doppler effect; Doppler frequency distribution; Imaging; Standards; Time-frequency analysis; Ultrafast Doppler; Ultrafast imaging; Ultrasonic imaging; biomedical ultrasonics; carotid artery plaque; diseases; flow profile; geometric broadening; sonography; spatiotemporal distribution; spatiotemporal phenomena; statistical technique; turbulece; turbulence; ultrafast plane wave imaging; vascular disease diagnosis
Composite media mixing Bragg and local resonances for highly attenuating and broad bandgaps Kaina, N., M. Fink, and G. Lerosey Scientific Reports 3 (2013) Résumé: In this article, we investigate composite media which present both a local resonance and a periodic structure. We numerically and experimentally consider the case of a very academic and simplified system that is a quasi-one dimensional split ring resonator medium. We modify its periodicity to shift the position of the Bragg bandgap relative to the local resonance one. We observe that for a well-chosen lattice constant, the local resonance frequency matches the Bragg frequency thus opening a single bandgap which is at the same time very wide and strongly attenuating. We explain this interesting phenomenon by the dispersive nature of the unit cell of the medium, using an analogy with the concept of white light cavities. Our results provide new ways to design wide and efficient bandgap materials.
Controlling light in scattering media non-invasively using the photoacoustic transmission matrix Chaigne, T., O. Katz, A. C. Boccara, M. Fink, E. Bossy, and S. Gigan Nature Photonics 8, 58-64 (2014) Résumé: Optical wavefront shaping has emerged as a powerful tool for manipulating light in strongly scattering media. It enables diffraction-limited focusing and imaging at depths where conventional microscopy techniques fail. However, to date, most examples of wavefront shaping have relied on direct access to the targets or implanted probes, and the challenge is to apply it non-invasively inside complex samples. Recently, ultrasonic-tagging techniques have been utilized successfully, but these allow only small acoustically tagged volumes to be addressed at each measurement. Here, we introduce an approach that allows the non-invasive measurement of an optical transmission matrix over a large volume, inside complex samples, using a standard photoacoustic imaging set-up. We demonstrate the use of this matrix for detecting, localizing and selectively focusing light on absorbing targets through diffusive samples, as well as for extracting the scattering medium properties. Combining the transmission-matrix approach with the advantages of photoacoustic imaging opens a path towards deep-tissue imaging and light delivery utilizing endogenous optical contrast.
Global approach for transient shear wave inversion based on the adjoint method: A comprehensive 2D simulation study Arnal, B., G. Pinton, P. Garapon, M. Pernot, M. Fink, and M. Tanter Physics in Medicine and Biology 58, no. 19, 6765-6778 (2013) Résumé: Shear wave imaging (SWI) maps soft tissue elasticity by measuring shear wave propagation with ultrafast ultrasound acquisitions (10 000 frames s -1). This spatiotemporal data can be used as an input for an inverse problem that determines a shear modulus map. Common inversion methods are local: the shear modulus at each point is calculated based on the values of its neighbour (e.g. time-of-flight, wave equation inversion). However, these approaches are sensitive to the information loss such as noise or the lack of the backscattered signal. In this paper, we evaluate the benefits of a global approach for elasticity inversion using a least-squares formulation, which is derived from full waveform inversion in geophysics known as the adjoint method. We simulate an acoustic waveform in a medium with a soft and a hard lesion. For this initial application, full elastic propagation and viscosity are ignored. We demonstrate that the reconstruction of the shear modulus map is robust with a non-uniform background or in the presence of noise with regularization. Compared to regular local inversions, the global approach leads to an increase of contrast (∼+3 dB) and a decrease of the quantification error (∼+2%). We demonstrate that the inversion is reliable in the case when there is no signal measured within the inclusions like hypoechoic lesions which could have an impact on medical diagnosis. © 2013 Institute of Physics and Engineering in Medicine. Mots-clés: Acoustic waveform; Backscattered signal; Full-waveform inversion; Global approaches; Inversion methods; Least-squares formulation; Shear wave imaging; Spatio-temporal data; Acoustics; Diagnosis; Elastic moduli; Elasticity; Inverse problems; Shear strain; Shear waves; Wave propagation; Least squares approximations
Transverse localization of sound Bretagne, A., M. Fink, and A. Tourin Physical Review B - Condensed Matter and Materials Physics 88, no. 10 (2013) Résumé: We show how disorder can be used to guide a broadband ultrasonic wave. The idea is to exploit the transverse localization regime that has been reported for light. Our waveguide consists of a set of parallel cylindrical scatterers randomly distributed in the transverse plane. An ultrasonic beam propagating along the direction of scatterers is found to remain confined in the two other directions on a size smaller than the waveguide diameter and driven by the localization length. Interestingly, the guided wave is also found to propagate with a very limited temporal dispersion. © 2013 American Physical Society.
Transcranial high intensity focused ultrasound therapy guided by 7 TESLA MRI in a rat brain tumour model: A feasibility study Dervishi, E., B. Larrat, M. Pernot, C. Adam, Y. Marie, M. Fink, J.-Y. Delattre, A.-L. Boch, M. Tanter, and J.-F. Aubry International Journal of Hyperthermia 29, no. 6, 598-608 (2013) Résumé: Purpose: Transcranial high intensity focused ultrasound (HIFU) therapy guided by magnetic resonance imaging (MRI) is a promising approach for the treatment of brain tumours. Our objective is to validate a dedicated therapy monitoring system for rodents for transcranial HIFU therapy under MRI guidance in an in vivo brain tumour model. Materials and methods: A dedicated MR-compatible ultrasound therapy system and positioning frame was developed. Three MR-compatible prefocused ultrasonic monoelement transducers were designed, operating at 1.5 MHz and 2.5 MHz with different geometries. A full protocol of transcranial HIFU brain therapy under MRI guidance was applied in n = 19 rats without and n = 6 rats with transplanted tumours (RG2). Different heating strategies were tested. After treatment, histological study of the brain was performed in order to confirm thermal lesions. Results: Relying on a larger aperture and a higher frequency, the 2.5 MHz transducer was found to give better results than other ones. This single element transducer optimised the ratio of the temperature elevation at the focus to the one at the skull surface. Using optimised transducer and heating strategies enabled thermal necrosis both in normal and tumour tissues as verified by histology while limiting overheating in the tissues in contact with the skull. Conclusions: In this study, a system for transcranial HIFU therapy guided by MRI was developed and tested in an in vivo rat brain tumour model. The feasibility of this therapy set-up to induce thermal lesions within brain tumours was demonstrated. © 2013 Informa UK Ltd. Mots-clés: Brain surgery; High intensity focused ultrasound; Magnetic resonance guided focused ultrasound surgery; Rat brain tumours; Thermal necrosis
Influence of the pressure field distribution in transcranial ultrasonic neurostimulation Younan, Y., T. Deffieux, B. Larrat, M. Fink, M. Tanter, and J.-F. Aubry Medical Physics 40, no. 8 (2013) Résumé: Purpose: Low-intensity focused ultrasound has been shown to stimulate the brain noninvasively and without noticeable tissue damage. Such a noninvasive and localized neurostimulation is expected to have a major impact in neuroscience in the coming years. This emerging field will require many animal experiments to fully understand the link between ultrasound and stimulation. The primary goal of this paper is to investigate transcranial ultrasonic neurostimulation at low frequency (320 kHz) on anesthetized rats for different acoustic pressures and estimate the in situ pressure field distribution and the corresponding motor threshold, if any. The corresponding acoustic pressure distribution inside the brain, which cannot be measured in vivo, is investigated based on numerical simulations of the ultrasound propagation inside the head cavity, reproducing at best the experiments conducted in the first part, both in terms of transducer and head geometry and in terms of acoustic parameters. Methods: In this study, 37 ultrasonic neurostimulation sessions were achieved in rats (N = 8) using a 320 kHz transducer. The corresponding beam profile in the entire head was simulated in order to investigate the in situ pressure and intensity level as well as the spatial pressure distribution, thanks to a rat microcomputed tomography scan (CT)-based 3D finite differences time domain solver. Results: Ultrasound pulse evoked a motor response in more than 60% of the experimental sessions. In those sessions, the stimulation was always present, repeatable with a pressure threshold under which no motor response occurred. This average acoustic pressure threshold was found to be 0.68 ± 0.1 MPa (corresponding mechanical index, MI = 1.2 and spatial peak, pulse averaged intensity, Isppa = 7.5 W cm-2), as calibrated in free water. A slight variation was observed between deep anesthesia stage (0.77 ± 0.04 MPa) and light anesthesia stage (0.61 ± 0.03 MPa), assessed from the pedal reflex. Several kinds of motor responses were observed: movements of the tail, the hind legs, the forelimbs, the eye, and even a single whisker were induced separately. Numerical simulations of an equivalent experiment with identical acoustic parameters showed that the acoustic field was spread over the whole rat brain with the presence of several secondary pressure peaks. Due to reverberations, a 1.8-fold increase of the spatial peak, temporal peak acoustic pressure (Psptp) (±0.4 standard deviation), a 3.6-fold increase (±1.8) for the spatial peak, temporal peak acoustic intensity (Isptp), and 2.3 for the spatial peak, pulse averaged acoustic intensity (Isppa), were found compared to simulations of the beam in free water. Applying such corrections due to reverberations on the experimental results would yield a higher estimation for the average acoustic pressure threshold for motor neurostimulation at 320 KHz at 1.2 ± 0.3 MPa (MI = 2.2 ± 0.5 and Isppa = 17.5 ± 7.5 W cm-2). Conclusions: Transcranial ultrasonic stimulation is pressure- and anesthesia-dependent in the rat model. Numerical simulations have shown that the acoustic pattern can be complex inside the rat head and that special care must be taken for small animal studies relating acoustic parameters to neurostimulation effects, especially at a low frequency. © 2013 American Association of Physicists in Medicine. Mots-clés: in vivo; neuromodulation; neurostimulation; ultrasound
Green's function retrieval and passive imaging from correlations of wideband thermal radiations Davy, M., M. Fink, and J. De Rosny Physical Review Letters 110, no. 20 (2013) Résumé: We present an experimental demonstration of electromagnetic Green's function retrieval from thermal radiations in anechoic and reverberant cavities. The Green's function between two antennas is estimated by cross correlating milliseconds of decimeter noise. We show that the temperature dependence of the cross-correlation amplitude is well predicted by the blackbody theory in the Rayleigh-Jeans limit. The effect of a nonuniform temperature distribution on the cross-correlation time symmetry is also explored. Finally, we open a new way to image scatterers using ambient thermal radiations. © 2013 American Physical Society. Mots-clés: Cross correlations; Experimental demonstrations; Green's function retrieval; Passive imaging; Temperature dependence; Wide-band; Green's function; Temperature distribution; Heat radiation
Targeting accuracy of transcranial magnetic resonance-guided high-intensity focused ultrasound brain therapy: A fresh cadaver model: Laboratory investigation Chauvet, D., L. Marsac, M. Pernot, A.-L. Boch, R. Guillevin, N. Salameh, L. Souris, L. Darrasse, M. Fink, M. Tanter, and J.-F. Aubry Journal of Neurosurgery 118, no. 5, 1046-1052 (2013) Résumé: Object. This work aimed at evaluating the accuracy of MR-guided high-intensity focused ultrasound (MRgHIFU) brain therapy in human cadaver heads. Methods. Eighteen heads of fresh human cadavers were removed with a dedicated protocol preventing intracerebral air penetration. The MR images allowed determination of the ultrasonic target: a part of the thalamic nucleus ventralis intermedius implicated in essential tremor. Osseous aberrations were corrected with simulation-based time reversal by using CT data from the heads. The ultrasonic session was performed with a 512-element phased-array transducer system operating at 1 MHz under stereotactic conditions with thermometric real-time MR monitoring performed using a 1.5-T imager. Results. Dissection, imaging, targeting, and planning have validated the feasibility of this human cadaver model. The average temperature elevation measured by proton resonance frequency shift was 7.9°C ± 3°C. Based on MRI data, the accuracy of MRgHIFU is 0.4 ± 1 mm along the right/left axis, 0.7 ± 1.2 mm along the dorsal/ventral axis, and 0.5 ± 2.4 mm in the rostral/caudal axis. Conclusions. Despite its limits (temperature, vascularization), the human cadaver model is effective for studying the accuracy of MRgHIFU brain therapy. With the 1-MHz system investigated here, there is millimetric accuracy. ©AANS, 2013. Mots-clés: Cadaver model; Focused ultrasound; Noninvasive brain therapy; Surgical technique; accuracy; article; brain; cadaver; computed tomography scanner; computer assisted tomography; dissection; essential tremor; high intensity focused ultrasound; human; imaging; magnetic resonance guided high intensity focused ultrasound; non invasive procedure; nuclear magnetic resonance imaging; nuclear magnetic resonance scanner; priority journal; real time ultrasound scanner; stereotactic procedure; temperature; t
Ultrasound elastography: Principles and techniques Gennisson, J.-L., T. Deffieux, M. Fink, and M. Tanter Diagnostic and Interventional Imaging (2013) Résumé: Ultrasonography has been widely used for diagnosis since it was first introduced in clinical practice in the 1970's. Since then, new ultrasound modalities have been developed, such as Doppler imaging, which provides new information for diagnosis. Elastography was developed in the 1990's to map tissue stiffness, and reproduces/replaces the palpation performed by clinicians. In this paper, we introduce the principles of elastography and give a technical summary for the main elastography techniques: from quasi-static methods that require a static compression of the tissue to dynamic methods that uses the propagation of mechanical waves in the body. Several dynamic methods are discussed: vibro-acoustography, Acoustic Radiation Force Impulsion (ARFI), transient elastography, shear wave imaging, etc. This paper aims to help the reader at understanding the differences between the different methods of this promising imaging modality that may become a significant tool in medical imaging. © 2013 Éditions françaises de radiologie. Mots-clés: Dynamic method; Impulse elastography; Quasi-static method; Shear wave elastography; Ultrasound elastography
EFSUMB Guidelines and Recommendations on the clinical use of ultrasound elastographypart 2: Clinical applications Cosgrove, D., F. Piscaglia, J. Bamber, J. Bojunga, J.-M. Correas, O. H. Gilja, A. S. Klauser, I. Sporea, F. Calliada, V. Cantisani, D', M. onofrio, E. E. Drakonaki, M. Fink, M. Friedrich-Rust, J. Fromageau, R. F. Havre, C. Jenssen, R. Ohlinger, A. Sǎftoiu, F. Schaefer, and C. F. Dietrich Ultraschall in der Medizin 34, no. 3, 238-253 (2013) Résumé: The clinical part of these Guidelines and Recommendations produced under the auspices of the European Federation of Societies for Ultrasound in Medicine and Biology EFSUMB assesses the clinically used applications of all forms of elastography, stressing the evidence from meta-analyses and giving practical advice for their uses and interpretation. Diffuse liver disease forms the largest section, reflecting the wide experience with transient and shear wave elastography. Then follow the breast, thyroid, gastro-intestinal tract, endoscopic elastography, the prostate and the musculo-skeletal system using strain and shear wave elastography as appropriate. The document is intended to form a reference and to guide clinical users in a practical way. © Georg Thieme Verlag KG Stuttgart, New York. Mots-clés: breast; elastography; liver; shear waves; stiffness; strain; thyroid; ultrasound
EFSUMB guidelines and recommendations on the clinical use of ultrasound elastographypart 1: Basic principles and technology Bamber, J., D. Cosgrove, C. F. Dietrich, J. Fromageau, J. Bojunga, F. Calliada, V. Cantisani, J.-M. Correas, D', M. onofrio, E. E. Drakonaki, M. Fink, M. Friedrich-Rust, O. H. Gilja, R. F. Havre, C. Jenssen, A. S. Klauser, R. Ohlinger, A. Saftoiu, F. Schaefer, I. Sporea, and F. Piscaglia Ultraschall in der Medizin 34, no. 2, 169-184 (2013) Résumé: The technical part of these Guidelines and Recommendations, produced under the auspices of EFSUMB, provides an introduction to the physical principles and technology on which all forms of current commercially available ultrasound elastography are based. A difference in shear modulus is the common underlying physical mechanism that provides tissue contrast in all elastograms. The relationship between the alternative technologies is considered in terms of the method used to take advantage of this. The practical advantages and disadvantages associated with each of the techniques are described, and guidance is provided on optimisation of scanning technique, image display, image interpretation and some of the known image artefacts. Mots-clés: elasticity; elastography; radiation force; shear modulus; shear wave; stiffness; strain; transient; ultrasonography
Subwavelength focusing inside an open disordered medium by time reversal at a single point antenna Pierrat, R., C. Vandenbem, M. Fink, and R. Carminati Physical Review A - Atomic, Molecular, and Optical Physics 87, no. 4 (2013) Résumé: We study theoretically light focusing at subwavelength scale inside a disordered strongly scattering open medium. We show that broadband time reversal at a single point antenna, in conjunction with near-field interactions and multiple scattering, produces spatial focusing with a quality comparable to that obtained in an ideal closed cavity. This provides different perspectives for super-resolved optical imaging and coherent control of single nanosources or absorbers in complex media. © 2013 American Physical Society. Mots-clés: Closed cavity; Coherent control; Disordered medium; Near field interactions; Optical imaging; Spatial focusing; Sub-wavelength focusing; Subwavelength scale; Antennas; Focusing
Ultra small mode volume defect cavities in spatially ordered and disordered metamaterials Kaina, N., F. Lemoult, M. Fink, and G. Lerosey Applied Physics Letters 102, no. 14 (2013) Résumé: In this letter, we study metamaterials made out of resonant electric wires arranged on a spatial scale much smaller than the free space wavelength, and we show that they present a hybridization band that is insensible to positional disorder. We experimentally demonstrate defect cavities in disordered and ordered samples and prove that, analogous to those designed in photonic crystals, those cavities can present very high quality factors. In addition, we show that they display mode volumes much smaller than a wavelength cube, owing to the deep subwavelength nature of the unit cell. We underline that this type of structure can be shrunk down to a period close of a few skin depth. Our approach paves the way towards the confinement and manipulation of waves at deep subwavelength scales in both ordered and disordered metamaterials. © 2013 AIP Publishing LLC. Mots-clés: Defect cavity; Display modes; Free-space wavelengths; High quality factors; Positional disorder; Spatial scale; Sub-wavelength; Subwavelength scale; Defects; Metamaterials
Elastography: A new modality of ultrasound imaging Fink, M. Diagnostic and Interventional Imaging (2013)
Acousto-optic imaging: Merging the best of two worlds Lerosey, G., and M. Fink Nature Photonics 7, no. 4, 265-267 (2013)
Functional ultrasound imaging of the brain: Theory and basic principles Mace, E., G. Montaldo, B.-F. Osmanski, I. Cohen, M. Fink, and M. Tanter IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 60, no. 3, 492-506 (2013) Résumé: Hemodynamic changes in the brain are often used as surrogates of neuronal activity to infer the loci of brain activity. A major limitation of conventional Doppler ultrasound for the imaging of these changes is that it is not sensitive enough to detect the blood flow in small vessels where the major part of the hemodynamic response occurs. Here, we present a μDoppler ultrasound method able to detect and map the cerebral blood volume (CBV) over the entire brain with an important increase in sensitivity. This method is based on imaging the brain at an ultrafast frame rate (1 kHz) using compounded plane wave emissions. A theoretical model demonstrates that the gain in sensitivity of the μDoppler method is due to the combination of 1) the high signal-to-noise ratio of the gray scale images, resulting from the synthetic compounding of backscattered echoes; and 2) the extensive signal averaging enabled by the high temporal sampling of ultrafast frame rates. This μDoppler imaging is performed in vivo on trepanned rats without the use of contrast agents. The resulting images reveal detailed maps of the rat brain vascularization with an acquisition time as short as 320 ms per slice. This new method is the basis for a real-time functional ultrasound (fUS) imaging of the brain. © 1986-2012 IEEE. Mots-clés: Backscattered echoes; Cerebral Blood Volume(CBV); Doppler ultrasound; Hemodynamic changes; Hemodynamic response; High signal-to-noise ratio; Neuronal activities; Theoretical models; Communication channels (information theory); Fading (radio); Hemodynamics; Non Newtonian flow; Ultrasonic imaging; Brain
Wave propagation control at the deep subwavelength scale in metamaterials Lemoult, F., N. Kaina, M. Fink, and G. Lerosey Nature Physics 9, no. 1, 55-60 (2013) Résumé: The ability to control wave propagation is of fundamental interest in many areas of physics. Photonic crystals proved very useful for this purpose but, because they are based on Bragg interferences, these artificial media require structures with large dimensions. Metamaterials, on the other hand, can exhibit very deep subwavelength spatial scales. In general they are studied for their bulk effective properties that lead to effects such as negative refraction. Here we go beyond this effective medium paradigm and we use a microscopic approach to study metamaterials based on resonant unit cells. We show that we can tailor unit cells locally to shape the flow of waves at deep subwavelength scales. We validate our approach in experiments with both electromagnetic and acoustic waves in the metre range demonstrating cavities, waveguides, corners and splitters with centimetre-scale dimensions, an order of magnitude smaller than previous proposals. © 2013 Macmillan Publishers Limited.
Analysis of the time reversal operator for a scatterer undergoing small displacements Philippe, F. D., C. Prada, M. Fink, J. Garnier, and J. De Rosny Journal of the Acoustical Society of America 133, no. 1, 94-107 (2013) Résumé: The method of the time reversal operator decomposition is usually employed to detect and characterize static targets using the invariants of the time reversal operator. This paper presents a theoretical and experimental investigation into the impact of small displacements of the target on these invariants. To find these invariants, the time reversal operator is built from the multistatic response matrix and then diagonalized. Two methods of recording the multistatic response matrix while the target is moving are studied: Acquisition either element by element or column by column. It is demonstrated that the target displacement generates new significant eigenvalues. Using a perturbation theory, the analytical expressions of the eigenvalues of the time-reversal operator for both acquisition methods are derived. We show that the distribution of the new eigenvalues strongly depends on these two methods. It is also found that for the column by column acquisition, the second eigenvector is simply linked to the scatterer displacements. At last, the implications on the Maximum Likelihood and Multiple Signal Classification detection are also discussed. The theoretical results are in good agreement with numerical and 3.4 MHz ultrasonic experiments. © 2013 Acoustical Society of America. Mots-clés: Analytical expressions; Eigenvalues; Element by elements; Experimental investigations; Multi-static; Multiple signal classification; Perturbation theory; Response matrices; Small displacement; Target displacement; Theoretical result; Time reversal operator decompositions; Time-reversal operator; Ultrasonic experiments; Mergers and acquisitions; Ultrasonic applications; Wavelet analysis; Eigenvalues and eigenfunctions; water; algorithm; article; computer simulation; equipment; equipment design; m
Ultrasound contrast plane wave imaging Couture, O., M. Fink, and M. Tanter IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 59, no. 12, 2676-2683 (2012) Résumé: Background: Monitoring the accumulation of microbubbles within tissue vasculature with ultrasound allows both molecular and perfusion imaging. Unfortunately, conventional imaging with focused pulses can destroy a large fraction of the microbubbles it is trying to follow. Using coherent synthetic summation, ultrafast plane wave imaging could attain similar image quality, while reducing the peak acoustic pressure and bubble disruption. Method: In these experiments, microbubbles were flowed in a wall-less vessel phantom. Images were obtained on a programmable clinical scanner with a set of line-per-line focused pulses for conventional contrast imaging and with compounded plane wave transmission adapted for nonlinear imaging. Imaging was performed between 14 and 650 kPa peak negative pressure at 7.5 MHz. The disruption of the microbubbles was evaluated by comparing the microbubble intensity before and after acquisition of a set of 100 images at various pressures. Results: The acoustic intensity required to disrupt 50% of the microbubbles was 24 times higher with plane-wave imaging compared with conventional focused pulses. Although both imaging approaches yield similar resolution, at the same disruption level, plane-wave imaging showed better contrast. In particular, at similar disruption ratio (50% after 100 images), contrast-pulse sequencing (CPS) performed with plane waves displayed an improvement of 11 dB compared with conventional nonlinear imaging. Conclusion: In each resolution cell of the image, plane-wave imaging spread the spatial peak acoustic intensity over more pulses, reducing the peak pressure and, hence, preserving the microbubbles. This method could contribute to molecular imaging by allowing the continuous monitoring of the accumulation of microbubbles with improved contrast. © 2012 IEEE. Mots-clés: Acoustic pressures; Clinical scanners; Continuous monitoring; Contrast imaging; Conventional imaging; Micro-bubble; Microbubbles; Negative pressures; Nonlinear imaging; Peak pressure; Perfusion imaging; Plane wave; Plane-wave transmission; Similar image; Ultra-fast; Ultrasound contrast; Vasculature; Vessel phantom; Acoustic intensity; Molecular imaging; Tissue; Ultrasonics; Elastic waves; agar; cellulose; contrast medium; article; echography; equipment; image processing; image quality; methodolo
Exploiting the time-reversal operator for adaptive optics, selective focusing and scattering pattern analysis Popoff, S. M., A. Aubry, G. Lerosey, M. Fink, A. C. Boccara, and S. Gigan 2012 Conference on Lasers and Electro-Optics, CLEO 2012 (2012) Résumé: We report on the optical measurement of the backscattering matrix in a weakly scattering medium. A decomposition of the time reversal operator allows selective and efficient focusing on individual scatterers, even through an aberrating layer. © 2012 OSA. Mots-clés: Backscattering matrix; Decomposition of the time reversal operator; Optical measurement; Scattering medium; Scattering pattern; Time-reversal operator; Lasers; Optical data processing; Scattering
Dispersion in media containing resonant inclusions: Where does it come from? Lemoult, F., M. Fink, and G. Lerosey 2012 Conference on Lasers and Electro-Optics, CLEO 2012 (2012) Résumé: Propagation media containing resonant inclusions have been studied for over a century in acoustics, electromagnetism or solid state physics. There exist some in nature, such as dielectrics, which contain enormous amounts of atoms. To calculate those materials permittivities one considers that each atom "sees" the same electromagnetic field and calculates the average field that takes into account an incoming wave as well as the overall response of the ensemble of atoms [1]. This macroscopic view assumes that there is no variations of the electromagnetic field at the scale of the inter-atomic distance. © 2012 OSA. Mots-clés: Average field; Inter-atomic distances; Propagation media; Electromagnetic fields; Lasers; Atoms
Optimal spatiotemporal focusing through complex scattering media Aulbach, J., A. Bretagne, M. Fink, M. Tanter, and A. Tourin 2012 Conference on Lasers and Electro-Optics, CLEO 2012 (2012) Résumé: We demonstrate, based on spatial and frequency resolved wave front shaping of ultrasound with a nonlinear feedback signal, how to achieve optimal spatiotemporal focusing through a complex scattering medium. © 2012 OSA. Mots-clés: Scattering media; Scattering medium; Spatiotemporal focusing; Wave front shaping; Lasers; Optimization
Monitoring the lesion formation during histotripsy treatment using shear wave imaging Arnal, B., W.-N. Lee, M. Pernot, M. Fink, and M. Tanter AIP Conference Proceedings 1503, 129-134 (2012) Résumé: Monitoring the lesion formation induced by histotripsy has mainly relied on the quantitative change in backscatter intensity using ultrasound B-mode imaging. However, how the mechanical properties of the histotripsy-treated tissue region alter during the procedure is yet to be fully investigated. We thus proposed here to monitor such a therapeutic process based on shear modulus estimated by shear wave imaging (SWI). In the therapeutic procedure, a single-element piezo-composite focused transducer (Imasonic, Besançon, France) with a center frequency of 660 kHz, a focal length of 45 mm, and an fnumber of 1 was driven by a function generator (AFG 3101, Tektronix, Beaverton, OR) and a gated RF power amplifier (GA-2500A, RITEC Inc., USA) to generate ultrasound histotripsy pulses. Histotripsy pulses were delivered for 20 seconds and then followed by a 30-second pause and a rapid monitoring step. Such a treatment and monitoring scheme was repeated for 10 mins. Both the reference measurement and monitoring were realized by SWI, where plane shear waves were generated by an 8 MHz linear array probe connected to a prototype ultrasound scanner, and acquired at a frame rate of 10000 Hz. Shear modulus was estimated and mapped in 2D through a time-of-flight algorithm. Gelatin (8%)-agar (2%) phantoms and ex-vivo porcine liver samples were tested. Regions of interests (ROI's) of 2 mm-by-2 mm in both untreated and treated regions were selected to compute the contrast-to-noise ratio (CNR). In all three scenarios where different PD's and PRF's were implemented, during the first 100 seconds of the treatment, 50% decrease in the shear modulus within the histotripsy-targeted zone was already observed, and the CNR of the shear modulus increased by 18 dB. In contrast, the backscatter intensity began to reduce and the corresponding CNR was found to increase by 6 dB only after 120 seconds of treatment. The results demonstrated that SWI can map quantitatively the change of mechanical properties during histotripsy treatment. Moreover, the shear modulus estimated by SWI was a more sensitive indicator of the lesion formation than the backscatter intensity obtained from B-mode at the early stage of the histotripsy treatment. In-vitro experiments on liver samples have also been carried out. © 2012 American Institute of Physics. Mots-clés: elastography; histotripsy; monitoring
The variance of quantitative estimates in shear wave imaging: Theory and experiments Deffieux, T., J.-L. Gennisson, B. Larrat, M. Fink, and M. Tanter IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 59, no. 11, 2390-2410 (2012) Résumé: In this paper, we investigate the relationship between the estimated shear modulus produced in shear wave imaging and the acquisition parameters. Using the framework of estimation theory and the Cramer¿Rao lower bound applied both to the estimation of the velocity field variance and to the estimation of the shear wave travel time, we can derive the analytical formulation of the shear modulus variance Σ2μ using relevant physical parameters such as the shear wave frequency, bandwidth, and ultrasonic parameters. This variance corresponds to the reproducibility of shear modulus reconstruction for a deterministic, quasi-homogeneous, and purely elastic medium. We thus consider the shear wave propagation as a deterministic process which is then corrupted during its observation by electronic noise and speckle decorrelation caused by shearing. A good correlation was found between analytical, numerical, and experimental results, which indicates that this formulation is well suited to understand the parameters¿ influence in those cases. The analytical formula stresses the importance of high-frequency and wideband shear waves for good estimation. Stiffer media are more difficult to assess reliably with identical acquisition signal-to-noise ratios, and a tradeoff between the reconstruction resolution of the shear modulus maps and the shear modulus variance is demonstrated. We then propose to use this formulation as a physical ground for a pixel-based quality measure that could be helpful for improving the reconstruction of real-time shear modulus maps for clinical applications. © 2012 IEEE. Mots-clés: Acquisition parameters; Analytical formulas; Analytical formulation; Clinical application; Deterministic process; Elastic medium; Electronic noise; Estimation theory; Good correlations; High frequency HF; Lower bounds; Modulus reconstruction; Physical parameters; Quality measures; Quantitative estimates; Reproducibilities; Shear wave imaging; Speckle decorrelation; Ultrasonic parameters; Velocity field; Wave frequencies; Wide-band; Elastic moduli; Estimation; Frequency estimation; Shear strain;
Time-reversal method and cross-correlation techniques by normal mode theory: A three-point problem Montagner, J.-P., C. Larmat, Y. Capdeville, M. Fink, H. Phung, B. Romanowicz, E. Clévédé, and H. Kawakatsu Geophysical Journal International 191, no. 2, 637-652 (2012) Résumé: Since its beginning in acoustics, the Time-Reversal method (hereafter referred as TR) has been explored by different studies to locate and characterize seismic sources in elastic media. But few authors have proposed an analytical analysis of the method, especially in the case of an elastic medium and for a finite body such as the Earth. In this paper, we use a normal mode approach (for general 3-D case and degenerate modes in 1-D reference model) to investigate the convergence properties of the TR method. We first investigate a three-point problem, with two fixed points which are the source and the receiver and a third one corresponding to a changing observation point. We extend the problem of a single channel TR experiment to a multiple channel and multiple station TR experiment. We show as well how this problem relates to the retrieval of Green's function with a multiple source cross-correlation and also the differences between TR method and cross-correlation techniques. Since most of the noise sources are located close to the surface of the Earth, we show that the time derivative of the cross-correlation of long-period seismograms with multiple sources at the surface is different from the Green's function. Next, we show the importance of a correct surface-area weighting of the signal resent by the stations according to a Voronoi tessellation of the Earth surface. We use arguments based on the stationary phase approximation to argue that phase-information is more important than amplitude information for getting a good focusing in TR experiment. Finally, by using linear relationships between the time-reversed displacement (resp. strain wavefields) and the components of a vector force source (resp. a moment tensor source), we show how to retrieve force (or moment tensor components) of any long period tectonic or environmental sources by time reversal. © 2012 The Authors Geophysical Journal International © 2012 RAS. Mots-clés: Earthquake source observations; Interferometry; Numerical solutions; Surface wave and free oscillations; Theoretical seismology; Time series analysis; Amplitude information; Analytical analysis; Convergence properties; Cross correlation techniques; Cross correlations; Degenerate modes; Earth surface; Earthquake source; Elastic media; Elastic medium; Finite bodies; Fixed points; Free oscillation; Linear relationships; Moment tensors; Multiple channels; Multiple source; Noise source; Normal mode t
Far field subwavelength imaging of magnetic patterns Ourir, A., G. Lerosey, F. Lemoult, M. Fink, and J. De Rosny Applied Physics Letters 101, no. 11 (2012) Résumé: Far field imaging of subwavelength magnetic objects in real time is a very challenging issue. We propose an original solution based on a planar array of closely spaced split ring resonators. Hybridization between the resonators of such metalens induces subwavelength modes with different frequencies. Thanks to these high Q resonating modes, Purcell like effect allows an evanescent source, close to the metalens, to emit waves that can be collected efficiently in the far field. We present the first microwave experimental demonstration of such metalens to image of a subwavelength magnetic pattern. Numerical simulation shows that this approach is still valid at THz frequencies. © 2012 American Institute of Physics. Mots-clés: Different frequency; Far field; Far-field imaging; Magnetic patterns; MetaLens; Planar arrays; Real time; Split ring resonator; Sub-wavelength; Subwavelength imaging; THz frequencies; Physical properties; Physics
Aberration correction by time reversal of moving speckle noise Osmanski, B.-F., G. Montaldo, M. Tanter, and M. Fink IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 59, no. 7, 1575-1583 (2012) Résumé: Focusing a wave through heterogeneous media is an important problem in medical ultrasound imaging. In such aberrating media, in the presence of a small number of point reflectors, iterative time reversal is a well-known method able to focus on the strongest reflector. However, in presence of speckle noise generated by many non-resolved scatterers, iterative time reversal alone does not work. In this paper, we propose the use of the echoes coming from moving particles in a flow, such as red blood cells, to generate a virtual point reflector by iterative time reversal. The construction of the virtual point reflector is performed by a coherent addition of independent realizations of speckle coming from moving particles. After focusing on a virtual point reflector, ultrasound images can be locally corrected inside an isoplanatic patch. An application for the correction of power Doppler images is presented. A theoretical analysis shows that this iterative method allows focusing on the point of maximal insonification of the uncorrected beam. © 1986-2012 IEEE. Mots-clés: Aberration correction; Coherent addition; Heterogeneous media; Isoplanatic patch; Medical ultrasound imaging; Moving particles; Point reflector; Power Doppler; Red blood cell; Speckle noise; Time reversal; Ultrasound images; Virtual points; Focusing; Reflection; Ultrasonic imaging; Speckle; algorithm; article; artifact; automated pattern recognition; computer assisted diagnosis; echography; flow kinetics; image enhancement; methodology; reproducibility; sensitivity and specificity; Algorithms; A
Time reversal of water waves Przadka, A., S. Feat, P. Petitjeans, V. Pagneux, A. Maurel, and M. Fink Physical Review Letters 109, no. 6 (2012) Résumé: We present time reversal experiments demonstrating refocusing of gravity-capillary waves in a water tank cavity. Owing to the reverberating effect of the cavity, only a few channels are sufficient to reconstruct the surface wave at the point source, even if the absorption is not negligible. Space-time-resolved measurements of the waves during the refocusing allow us to quantitatively demonstrate that the quality of the refocusing increases linearly with the number of reemitting channels. Numerical simulations corresponding to water waves at larger scales, with negligible damping, indicate the possibility of very high quality refocusing. © 2012 American Physical Society. Mots-clés: Gravity capillary waves; High quality; Point sources; Re-emitting; Time reversal; Surface waves; Water tanks; Water waves
Tunable time-reversal cavity for high-pressure ultrasonic pulses generation: A tradeoff between transmission and time compression Arnal, B., M. Pernot, M. Fink, and M. Tanter Applied Physics Letters 101, no. 6 (2012) Résumé: This Letter presents a time reversal cavity that has both a high reverberation time and a good transmission factor. A multiple scattering medium has been embedded inside a fluid-filled reverberating cavity. This allows creating smart ultrasonic sources able to generate very high pressure pulses at the focus outside the cavity with large steering capabilities. Experiments demonstrate a 25 dB gain in pressure at the focus. This concept will enable us to convert conventional ultrasonic imaging probes driven by low power electronics into high power probes for therapeutic applications requiring high pressure focused pulses, such as histotripsy or lithotripsy. © 2012 American Institute of Physics. Mots-clés: Fluid-filled; High pressure; High-power; Lithotripsy; Multiple-scattering medium; Reverberation time; Therapeutic Application; Time compression; Time reversal; Ultrasonic pulse; Ultrasonic sources; Architectural acoustics; Reverberation; Ultrasonic imaging; Probes
Monitoring of cornea elastic properties changes during UV-A/riboflavin-induced corneal collagen cross-linking using supersonic shear wave imaging: A pilot study Nguyen, T.-M., J.-F. Aubry, D. Touboul, M. Fink, J.-L. Gennisson, J. Bercoff, and M. Tanter Investigative Ophthalmology and Visual Science 53, no. 9, 5948-5954 (2012) Résumé: Purpose. Keratoconus disease or post-LASIK corneal ectasia are increasingly treated using UV-A/riboflavin-induced corneal collagen cross-linking (CXL). However, this treatment suffers from a lack of techniques to provide an assessment in real-time of the CXL effects. Here, we investigated the potential interest of corneal elasticity as a biomarker of the efficacy of this treatment. Methods. For this purpose, supersonic shear wave imaging (SSI) was performed both ex vivo and in vivo on porcine eyes before and after CXL. Based on ultrasonic scanners providing ultrafast frame rates (~30 kHz), the SSI technique generates and tracks the propagation of shear waves in tissues. It provides two- and three-dimensional (2-D and 3-D) quantitative maps of the corneal elasticity. Results. After CXL, quantitative maps of corneal stiffness clearly depicted the cross-linked area with a typical 200-μm lateral resolution. The CXL resulted in a 56% ± 15% increase of the shear wave speed for corneas treated in vivo (n = 4). Conclusions. The in vivo CXL experiments performed on pigs demonstrated that the quantitative estimation of local stiffness and the 2-D elastic maps of the corneal surface provide an efficient way to monitor the local efficacy of corneal cross-linking. © 2012 The Association for Research in Vision and Ophthalmology, Inc. Mots-clés: riboflavin; collagen; cross linking reagent; photosensitizing agent; riboflavin; animal experiment; animal model; animal tissue; article; controlled study; cornea; elasticity; elastography; imaging; in vivo study; nonhuman; pilot study; priority journal; protein cross linking; quantitative analysis; radiation; supersonic shear wave imaging; ultrasound; ultraviolet A radiation; animal; cornea; drug effect; echography; elasticity; elastography; metabolism; physiologic monitoring; physiology; swine
A polychromatic approach to far-field superlensing at visible wavelengths Lemoult, F., M. Fink, and G. Lerosey Nature Communications 3 (2012) Résumé: Breaking the diffraction barrier in the visible part of the electromagnetic spectrum is of fundamental importance. Far-field subwavelength focusing of light could, for instance, drastically broaden the possibilities available in nanolithography, light-matter interactions and sensing at the nanoscale. Similarly, imaging with a nanometric resolution could result in incredible breakthroughs in soft matter and biology. There have been numerous proposals in this regard based on metamaterials, structured illumination methods or diffractive optical components. The common denominator of all these approaches resides in their monochromatic nature. Here we show that using polychromatic light in dispersive metamaterials allows us to circumvent many limitations associated with previous monochromatic approaches. We design a plasmonic metalens based on metallic nanorods that, when used with broadband light fields, can beat the diffraction limit for imaging and focusing from the far field. © 2012 Macmillan Publishers Limited. All rights reserved. Mots-clés: nanomaterial; nanorod; article; diffraction; electromagnetic field; electromagnetic radiation; imaging system; lens; light; polychromatic light; spectral sensitivity
Hybridization band gap based smart antennas: Deep subwavelength yet directional and strongly decoupled MIMO antennas Lerosey, G., C. Leray, F. Lemoult, J. De Rosny, A. Tourin, and M. Fink Proceedings of 6th European Conference on Antennas and Propagation, EuCAP 2012, 2697-2701 (2012) Résumé: In this paper, we show how the concept of hybridization band gaps can be utilized to create antennas for MIMO applications. Those strongly decoupled antennas present at the same time a very small form factor and a very low correlation. To that aim, we first explain briefly the concept of hybridization between a resonator and the free space waves continuum. Then we expose the methodology we use to design multi-ports antennas based on that concept. We present numerical and experimental results of 2 ports MIMO antennas at 2.45 GHz, printed on a PCB, whose areas are smaller than 2.6*2.6 cm 2. The two ports display experimentally peak gains of a about 4 dB, efficiencies of 80%, a coupling lower than -30 dB and a correlation lower than 0.1. © 2012 IEEE. Mots-clés: compact antenna arrays; electromagnetic band gap antennas; metamaterials; MIMO antennas; photonic crystals; Smart antennas; Compact antenna; Electromagnetic band gap antennas; Free spaces; Low correlation; MIMO antenna; MIMO applications; Peak gain; Small form factors; Sub-wavelength; Approximation theory; Energy gap; Metamaterials; Photonic crystals; Smart antennas; Metamaterial antennas
Controlling waves in space and time for imaging and focusing in complex media Mosk, A. P., A. Lagendijk, G. Lerosey, and M. Fink Nature Photonics 6, no. 5, 283-292 (2012) Résumé: In complex media such as white paint and biological tissue, light encounters nanoscale refractive-index inhomogeneities that cause multiple scattering. Such scattering is usually seen as an impediment to focusing and imaging. However, scientists have recently used strongly scattering materials to focus, shape and compress waves by controlling the many degrees of freedom in the incident waves. This was first demonstrated in the acoustic and microwave domains using time reversal, and is now being performed in the optical realm using spatial light modulators to address the many thousands of spatial degrees of freedom of light. This approach is being used to investigate phenomena such as optical super-resolution and the time reversal of light, thus opening many new avenues for imaging and focusing in turbid media. © 2012 Macmillan Publishers Limited. All rights reserved.
Application of 1-d transient elastography for the shear modulus assessment of thin-layered soft tissue: Comparison with supersonic shear imaging technique Brum, J., J.-L. Gennisson, T.-M. Nguyen, N. Benech, M. Fink, M. Tanter, and C. Negreira IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 59, no. 4, 703-714 (2012) Résumé: Elasticity estimation of thin-layered soft tissues has gained increasing interest propelled by medical applications like skin, corneal, or arterial wall shear modulus assessment. In this work, the authors propose one-dimensional transient elastography (1DTE) for the shear modulus assessment of thin-layered soft tissue. Experiments on three phantoms with different elasticities and plate thicknesses were performed. First, using 1DTE, the shear wave speed dispersion curve inside the plate was obtained and validated with finite difference simulation. No dispersive effects were observed and the shear wave speed was directly retrieved from time-of-flight measurements. Second, the supersonic shear imaging (SSI) technique (considered to be a gold standard) was performed. For the SSI technique, the propagating wave inside the plate is guided as a Lamb wave. Experimental SSI dispersion curves were compared with finite difference simulation and fitted using a generalized Lamb model to retrieve the plate bulk shear wave speed. Although they are based on totally different mechanical sources and induce completely different diffraction patterns for the shear wave propagation, the 1DTE and SSI techniques resulted in similar shear wave speed estimations. The main advantage of the 1DTE technique is that bulk shear wave speed can be directly retrieved without requiring a dispersion model. © 2012 IEEE. Mots-clés: Arterial wall; Dispersion curves; Dispersion models; Dispersive effects; Elasticity estimation; Finite difference simulations; Gold standards; Shear wave speed; Shear wave speed estimation; Soft tissue; Supersonic shear imaging; Time of flight measurements; Transient elastography; Elastic moduli; Elasticity; Medical applications; Medical imaging; Rating; Shear strain; Speed; Tissue; Shear waves; algorithm; article; biological model; biomechanics; comparative study; elastography; finite element a
Mapping myocardial fiber orientation using echocardiography-based shear wave imaging Lee, W.-N., M. Pernot, M. Couade, E. Messas, P. Bruneval, A. Bel, A. A. Hagège, M. Fink, and M. Tanter IEEE Transactions on Medical Imaging 31, no. 3, 554-562 (2012) Résumé: The assessment of disrupted myocardial fiber arrangement may help to understand and diagnose hypertrophic or ischemic cardiomyopathy. We hereby proposed and developed shear wave imaging (SWI), which is an echocardiography-based, noninvasive, real-time, and easy-to-use technique, to map myofiber orientation. Five in vitro porcine and three in vivo open-chest ovine hearts were studied. Known in physics, shear wave propagates faster along than across the fiber direction. SWI is a technique that can generate shear waves travelling in different directions with respect to each myocardial layer. SWI further analyzed the shear wave velocity across the entire left-ventricular (LV) myocardial thickness, ranging between 10 (diastole) and 25 mm (systole), with a resolution of 0.2 mm in the middle segment of the LV anterior wall region. The fiber angle at each myocardial layer was thus estimated by finding the maximum shear wave speed. In the in vitro porcine myocardium (n=5), the SWI-estimated fiber angles gradually changed from +80° ± 7° (endocardium) to +30° ± 13° (midwall) and-40° ± 10° (epicardium) with 0° aligning with the circumference of the heart. This transmural fiber orientation was well correlated with histology findings (r 2=0.91± 0.02, p<0.0001). SWI further succeeded in mapping the transmural fiber orientation in three beating ovine hearts in vivo. At midsystole, the average fiber orientation exhibited 71° ± 13° (endocardium), 27° ± 8° (midwall), and-26° ± 30° (epicardium). We demonstrated the capability of SWI in mapping myocardial fiber orientation in vitro and in vivo. SWI may serve as a new tool for the noninvasive characterization of myocardial fiber structure. © 2011 IEEE. Mots-clés: Anisotropy; echocardiography; fiber; myocardium; shear wave; Fiber angles; Fiber arrangement; Fiber direction; Fiber structures; In-vitro; In-vivo; Maximum shears; myocardium; Shear wave imaging; Shear wave velocity; Wall region; Anisotropy; Echocardiography; Fibers; Heart; Mapping; Shear waves; animal; anisotropy; article; cytology; echocardiography; heart; heart muscle; heart muscle cell; histology; image processing; methodology; physiology; sheep; signal processing; swine; Animals; Anisotropy
MR-guided adaptive focusing of therapeutic ultrasound beams in the human head Marsac, L., D. Chauvet, B. Larrat, M. Pernot, B. Robert, M. Fink, A. L. Boch, J. F. Aubry, and M. Tanter Medical Physics 39, no. 2, 1141-1149 (2012) Résumé: Purpose: This study aims to demonstrate, using human cadavers the feasibility of energy-based adaptive focusing of ultrasonic waves using magnetic resonance acoustic radiation force imaging (MR-ARFI) in the framework of non-invasive transcranial high intensity focused ultrasound (HIFU) therapy. Methods: Energy-based adaptive focusing techniques were recently proposed in order to achieve aberration correction. The authors evaluate this method on a clinical brain HIFU system composed of 512 ultrasonic elements positioned inside a full body 1.5 T clinical magnetic resonance (MR) imaging system. Cadaver heads were mounted onto a clinical Leksell stereotactic frame. The ultrasonic wave intensity at the chosen location was indirectly estimated by the MR system measuring the local tissue displacement induced by the acoustic radiation force of the ultrasound (US) beams. For aberration correction, a set of spatially encoded ultrasonic waves was transmitted from the ultrasonic array and the resulting local displacements were estimated with the MR-ARFI sequence for each emitted beam. A noniterative inversion process was then performed in order to estimate the spatial phase aberrations induced by the cadaver skull. The procedure was first evaluated and optimized in a calf brain using a numerical aberrator mimicking human skull aberrations. The full method was then demonstrated using a fresh human cadaver head. Results: The corrected beam resulting from the direct inversion process was found to focus at the targeted location with an acoustic intensity 2.2 times higher than the conventional non corrected beam. In addition, this corrected beam was found to give an acoustic intensity 1.5 times higher than the focusing pattern obtained with an aberration correction using transcranial acoustic simulation-based on X-ray computed tomography (CT) scans. Conclusions: The proposed technique achieved near optimal focusing in an intact human head for the first time. These findings confirm the strong potential of energy-based adaptive focusing of transcranial ultrasonic beams for clinical applications. © 2012 American Association of Physicists in Medicine. Mots-clés: adaptive focusing; HIFU; MR-ARFI; MRI; ultrasound transcranial therapy; animal; article; brain; cattle; computer assisted surgery; feasibility study; high intensity focused ultrasound; human; interventional magnetic resonance imaging; methodology; pathology; treatment outcome; Animals; Brain; Cattle; Feasibility Studies; High-Intensity Focused Ultrasound Ablation; Humans; Magnetic Resonance Imaging, Interventional; Surgery, Computer-Assisted; Treatment Outcome
Imaging changes in scattering media from Time Reversal of the Coda wave Difference (TRECOD) Bonneau, L., C. Prada, M. Fink, and A. Tourin Waves in Random and Complex Media 22, no. 1, 109-120 (2012) Résumé: We propose a new method for monitoring temporal changes in a complex scattering environment. It is referred to as Time Reversal of the Coda wave Difference (TRECOD). The impulse responses of the probed medium are recorded between all the emitter/receiver pairs of a transceiver array. A Fourier transform of these responses then produces the so-called backscattering transfer matrix at each frequency of the transceiver bandwidth. The matrix acquisition is repeated and the image of the temporal changes occurring between two matrix acquisitions is formed by propagating numerically the significant singular vectors of the matrix difference. Small-scale experiments with ultrasound are used to validate the method and demonstrate its interest for the monitoring of a fluid injection in a porous medium behind a strongly scattering obstacle. © 2012 Copyright Taylor and Francis Group, LLC. Mots-clés: Coda waves; Fluid injections; matrix; Porous medium; Scattering environment; Scattering media; Singular vectors; Small-scale experiment; Temporal change; Time reversal; Transceiver array; Transfer matrixes; Porous materials; Transceivers; Transfer matrix method; Scattering
Optimal spatiotemporal focusing through complex scattering media Aulbach, J., A. Bretagne, M. Fink, M. Tanter, and A. Tourin Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 85, no. 1 (2012) Résumé: We present an alternative approach for spatiotemporal focusing through complex scattering media by wave front shaping. Using a nonlinear feedback signal to shape the incident pulsed wave front, we show that the limit of a spatiotemporal matched filter can be achieved; i.e., the wave amplitude at the intended time and focus position is maximized for a given input energy. It is exactly what is also achieved with time reversal. Demonstrated with ultrasound experiments, our method is generally applicable to all types of waves. © 2012 American Physical Society. Mots-clés: Alternative approach; Focus positions; Input energy; Pulsed wave; Scattering media; Spatiotemporal focusing; Time reversal; Wave amplitudes; Wave front shaping; Condensed matter physics; Physics; Wavefronts
Numerical prediction of frequency dependent 3D maps of mechanical index thresholds in ultrasonic brain therapy Pinton, G., J.-F. Aubry, M. Fink, and M. Tanter Medical Physics 39, no. 1, 455-467 (2012) Résumé: Purpose: Therapeutic ultrasound has been used in the brain for thrombolysis and high intensity focused ultrasound (HIFU) therapy. A low-frequency clinical study of sonothrombolysis, called the transcranial low-frequency ultrasound-mediated thrombolysis in brain ischemia (TRUMBI), has revealed an increased incidence of hemorrhage, which may have been caused by cavitation. The goal of this study is to determine if there is a comparable risk of generating cavitation during HIFU brain therapy at different frequencies. Methods: Two approaches are used to transmit acoustic energy through the skull to the brain: low-frequency ultrasound, with a wavelength that is larger than the skull thickness, and high frequency ultrasound, that is sensitive to aberrations and must use corrective techniques. At high frequency, the mechanical index (MI) is lower, which translates to a higher cavitation threshold. In addition to the nonfocused geometry of the 300 kHz sonothrombolysis treatment device, two types of focused therapeutic transducers were modeled: a low frequency 220 kHz transducer and a 1 MHz transducer that required aberration correction with a time-reversal approach, representing the lowest and highest frequencies currently used. The acoustic field was modeled with a finite difference fullwave acoustic code developed for large scale computations, that is, capable of simulating the entire brain volume. Various MI thresholds and device geometries were considered to determine the regions of the brain that have an increased probability of cavitation events. Results: For an equivalent energy deposition rate, it is shown that at a low frequency there is a significant volume of the brain that is above the MI thresholds. At a high frequency, the volume is over 3 orders of magnitude smaller, and it is entirely confined to a compact focal spot. Conclusions: The significant frequency dependence of the volumes with an increased probability of cavitation can be attributed to two factors: First, the volume encompassed by the focal region depends on the cube of the frequency. Second, the heat deposition increases with frequency. In conclusion, according to these simulations, the acoustic environment during HIFU brain therapy at 1 MHz is not conducive to a high probability of cavitation in extended regions of the brain. © 2012 American Association of Physicists in Medicine. Mots-clés: cavitation; HIFU; thrombolysis; ultrasound brain therapy; animal; article; biological model; brain; computer simulation; differential threshold; high intensity focused ultrasound; human; methodology; physiology; pressure; radiation; radiation dose; radiation exposure; radiation response; Animals; Brain; Computer Simulation; Differential Threshold; Dose-Response Relationship, Radiation; High-Energy Shock Waves; High-Intensity Focused Ultrasound Ablation; Humans; Models, Biological; Pressure; Radi
Exploiting the time-reversal operator for adaptive optics, selective focusing, and scattering pattern analysis Popoff, S. M., A. Aubry, G. Lerosey, M. Fink, A. C. Boccara, and S. Gigan Physical Review Letters 107, no. 26 (2011) Résumé: We report on the experimental measurement of the backscattering matrix of a weakly scattering medium in optics, composed of a few dispersed gold nanobeads. The decomposition of the time-reversal operator is applied to this matrix and we demonstrate selective and efficient focusing on individual scatterers, even through an aberrating layer. Moreover, we show that this approach provides the decomposition of the scattering pattern of a single nanoparticle. These results open important perspectives for optical imaging, characterization, and selective excitation of nanoparticles. © 2011 American Physical Society. Mots-clés: Backscattering matrix; Experimental measurements; matrix; Nanobeads; Optical imaging; Scattering medium; Scattering pattern; Selective excitations; Single nanoparticle; Time-reversal operator; Nanoparticles; Scattering
Microbubble ultrasound super-localization imaging (MUSLI) Couture, O., B. Besson, G. Montaldo, M. Fink, and M. Tanter IEEE International Ultrasonics Symposium, IUS, 1285-1287 (2011) Résumé: When distinct sources are generated in a region of interest, their location can be mapped with a resolution beyond the diffraction limit. Such distinct sources can be generated during ultrafast imaging of clouds of clinical contrast agents at the appropriate acoustic pressures. This paper describes experiments on the resolution limit, in-vitro localization of microbubbles and the demonstration that ultrafast events are present in-vivo. Mapping distinct events could yield images of vasculature at the micrometer scale. © 2011 IEEE. Mots-clés: imaging; localization; Microbubbles; super-resolution; Acoustic pressures; Contrast agent; Diffraction limits; In-vitro; In-vivo; localization; Micro-bubble; Microbubbles; Micrometer scale; Region of interest; Resolution limits; Super resolution; Ultrafast events; Ultrafast imaging; Vasculature; Acoustics; Imaging techniques; Ultrasonics; Diffraction
Controlling light through optical disordered media: Transmission matrix approach Popoff, S. M., G. Lerosey, M. Fink, A. C. Boccara, and S. Gigan New Journal of Physics 13 (2011) Résumé: We experimentally measure the monochromatic transmission matrix (TM) of an optical multiple scattering medium using a spatial light modulator together with a phase-shifting interferometry measurement method. The TM contains all the information needed to shape the scattered output field at will or to detect an image through the medium. We confront theory and experiment for these applications and study the effect of noise on the reconstruction method. We also extracted from the TM information about the statistical properties of the medium and the light transport within it. In particular, we are able to isolate the contributions of the memory effect and measure its attenuation length. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Mots-clés: Attenuation lengths; Disordered media; Light transport; Memory effects; Multiple-scattering medium; Phase shifting Interferometry; Reconstruction method; Spatial light modulators; Statistical properties; Transmission matrix; Light modulators; Light transmission
One channel acoustic 3D imaging device of large aperture working in echographic mode Etaix, N., R.-K. Ing, and M. Fink 18th International Congress on Sound and Vibration 2011, ICSV 2011 2, 1570-1576 (2011) Résumé: Imaging devices generally use a 1D or 2D array of transducers to focus anywhere acoustic waves in space. The resolution of such systems depends on the aperture of the array. However, these systems require a large number of transducers to get optimal aperture and then complex multichannel electronics to control the focalization. In this work, an alternative one channel imaging device is proposed. It uses only one piezoelectric transducer glued to an aluminium plate of non-regular geometry. The plate is used as an acoustic cavity which mixes the flexural waves emitted by the transducer. Part of waves radiates into the air and the plate is then comparable to an acoustic aperture of large dimension. In emission mode, the focusing process is realized over a large frequency bandwidth -from 5 kHz to 100 kHz. To focus acoustic waves anywhere in front of the plate, the electric impulse responses used to drive the piezoelectric transducer are computed from the knowledge of the vibration patterns of the plate. For a given focusing position a corresponding impulse response is computed. Finally beam steering is achieved and the acoustic waves should be focused anywhere in front of the plate. This result is comparable to a 2D transducer array. Finally, using a single microphone receiver working in echographic mode our imaging device is able to locate any object placed in front of it. Copyright © (2011) by the International Institute of Acoustics & Vibration. Mots-clés: 2D arrays; 3D imaging; Acoustic cavities; Aluminium plates; Beam-steering; Emission modes; Frequency band width; Imaging device; Large aperture; Large dimensions; Multi-channel; Transducer array; Vibration pattern; Acoustic fields; Acoustic waves; Imaging techniques; Impulse response; Piezoelectric transducers; Vibrations (mechanical)
Time reversal in subwavelength-scaled resonant media: Beating the diffraction limit Lemoult, F., A. Ourir, J. De Rosny, A. Tourin, M. Fink, and G. Lerosey International Journal of Microwave Science and Technology (2011) Résumé: Time reversal is a physical concept that can focus waves both spatially and temporally regardless of the complexity of the propagation medium. Time reversal mirrors have been demonstrated first in acoustics, then with electromagnetic waves, and are being intensively studied in many fields ranging from underwater communications to sensing. In this paper, we will review the principles of time reversal and in particular its ability to focus waves in complex media. We will show that this focusing effect depends on the complexity of the propagation medium rather than on the time reversal mirror itself. A modal approach will be utilized to explain the physical mechanism underlying the concept. A particular focus will be given on the possibility to break the diffraction barrier from the far field using time reversal. We will show that finite size media made out of coupled subwavelength resonators support modes which can radiate efficiently in the far field spatial information of the near field of a source. We will show through various examples that such a process, due to reversibility, permits to beat the diffraction limit using far field time reversal, and especially that this result occurs owing to the broadband inherent nature of time reversal. © 2011 Fabrice Lemoult et al.
Optimal transcostal high-intensity focused ultrasound with combined real-time 3D movement tracking and correction Marquet, F., J. F. Aubry, M. Pernot, M. Fink, and M. Tanter Physics in Medicine and Biology 56, no. 22, 7061-7080 (2011) Résumé: Recent studies have demonstrated the feasibility of transcostal high intensity focused ultrasound (HIFU) treatment in liver. However, two factors limit thermal necrosis of the liver through the ribs: the energy deposition at focus is decreased by the respiratory movement of the liver and the energy deposition on the skin is increased by the presence of highly absorbing bone structures. Ex vivo ablations were conducted to validate the feasibility of a transcostal real-time 3D movement tracking and correction mode. Experiments were conducted through a chest phantom made of three human ribs immersed in water and were placed in front of a 300 element array working at 1 MHz. A binarized apodization law introduced recently in order to spare the rib cage during treatment has been extended here with real-time electronic steering of the beam. Thermal simulations have been conducted to determine the steering limits. In vivo 3D-movement detection was performed on pigs using an ultrasonic sequence. The maximum error on the transcostal motion detection was measured to be 0.09 0.097 mm on the anterior-posterior axis. Finally, a complete sequence was developed combining real-time 3D transcostal movement correction and spiral trajectory of the HIFU beam, allowing the system to treat larger areas with optimized efficiency. Lesions as large as 1 cm in diameter have been produced at focus in excised liver, whereas no necroses could be obtained with the same emitted power without correcting the movement of the tissue sample. © 2011 Institute of Physics and Engineering in Medicine. Mots-clés: article; breathing; echography; evaluation; feasibility study; human; image quality; liver; methodology; movement (physiology); reproducibility; rib; skin; three dimensional imaging; time; ultrasound therapy; Feasibility Studies; Humans; Imaging, Three-Dimensional; Liver; Movement; Phantoms, Imaging; Reproducibility of Results; Respiration; Ribs; Skin; Time Factors; Ultrasonic Therapy; Ultrasonography; Anterior posteriors; Apodizations; Bone structure; Chest phantom; Electronic steering; Element
In vivo bubble nucleation probability in sheep brain tissue Gateau, J., J.-F. Aubry, D. Chauvet, A.-L. Boch, M. Fink, and M. Tanter Physics in Medicine and Biology 56, no. 22, 7001-7015 (2011) Résumé: Gas nuclei exist naturally in living bodies. Their activation initiates cavitation activity, and is possible using short ultrasonic excitations of high amplitude. However, little is known about the nuclei population in vivo, and therefore about the rarefaction pressure required to form bubbles in tissue. A novel method dedicated to in vivo investigations was used here that combines passive and active cavitation detection with a multi-element linear ultrasound probe (4-7 MHz). Experiments were performed in vivo on the brain of trepanated sheep. Bubble nucleation was induced using a focused single-element transducer (central frequency 660 kHz, f-number = 1) driven by a high power (up to 5 kW) electric burst of two cycles. Successive passive recording and ultrafast active imaging were shown to allow detection of a single nucleation event in brain tissue in vivo. Experiments carried out on eight sheep allowed statistical studies of the bubble nucleation process. The nucleation probability was evaluated as a function of the peak negative pressure. No nucleation event could be detected with a peak negative pressure weaker than -12.7 MPa, i.e. one order of magnitude higher than the recommendations based on the mechanical index. Below this threshold, bubble nucleation in vivo in brain tissues is a random phenomenon. © 2011 Institute of Physics and Engineering in Medicine. Mots-clés: Active cavitation detection; Active imaging; Brain tissue; Bubble nucleation; Cavitation activity; Central frequency; High amplitudes; High-power; In-vivo; Living bodies; Mechanical indexes; Multi-element; Negative pressures; Novel methods; Single element transducers; Statistical study; Ultra-fast; Ultrasonic excitation; Ultrasound probes; Brain; Cavitation; Experiments; Tissue; Ultrasonic applications; Ultrasonics; Wool; Nucleation; animal; animal disease; article; brain; calibration; chemistry
Revisiting the wire medium: An ideal resonant metalens Lemoult, F., M. Fink, and G. Lerosey Waves in Random and Complex Media 21, no. 4, 591-613 (2011) Résumé: This article is the first one in a series of two dealing with the concept of a 'resonant metalens' we introduced recently. Here, we focus on the physics of a medium with finite dimensions consisting of a square lattice of parallel conducting wires arranged on a sub-wavelength scale. This medium supports electromagnetic fields that vary much faster than the operating wavelength. We show that such modes are dispersive due to the finiteness of the medium. Their dispersion relation is established in a simple way, a link with designer plasmons is made, and the canalization phenomenon is reinterpreted in the light of our model. We explain how to take advantage of this dispersion in order to code sub-wavelength wavefields in time. Finally, we show that the resonant nature of the medium ensures an efficient coupling of these modes with free space propagating waves and, thanks to the Purcell effect, with a source placed in the near field of the medium. © 2011 Taylor & Francis. Mots-clés: Conducting wire; Dispersion relations; Efficient coupling; Finite dimensions; Free space; MetaLens; Near fields; Operating wavelength; Purcell effect; Square lattices; Sub-wavelength; Wavefields; Wire medium; Electromagnetic fields; Wire; Dispersion (waves)
A multiwave imaging approach for elastography Fink, M., and M. Tanter Current Medical Imaging Reviews 7, no. 4, 340-349 (2011) Résumé: Interactions between waves can be turned into profit to break diffraction limits and invent new kinds of medical images. It consists in productively combining two very different waves -- one to provide contrast, another to provide spatial resolution -in order to build a new kind of image, Multiwave imaging provides a unique image of the most interesting contrast with the most interesting resolution. We will show in this paper how this general concept of multiwave imaging allow to perform high resolution and quantitative elasticity imaging of the human body. Here, the two waves are sonic shear waves and ultrasonic compressional waves. A comparison with static elastography (a single wave technique) will show the interest of multiwave imaging and various clinical examples will be presented to illustrate the efficiency of this approach. ©2011 Bentham Science Publishers. Mots-clés: Cancer; Elasticity; Elastography; Medical imaging; Radiology; Shear wave imaging; Ultrafast imaging; Ultrasound; article; breast cancer; cancer diagnosis; elastography; human; phantom; priority journal; radiation physics; sonic shear wave; spectroscopy; ultrasonic compressional wave; Young modulus
Far-field sub-wavelength imaging and focusing using a wire medium based resonant metalens Lemoult, F., M. Fink, and G. Lerosey Waves in Random and Complex Media 21, no. 4, 614-627 (2011) Résumé: This is the second article in a series of two dealing with the concept of a 'resonant metalens' we introduced recently. This is a new type of lens capable of coding in time and radiating efficiently in the far-field region sub-diffraction information about an object. A proof of the concept of such a lens is performed in the microwave range, using a medium made out of a square lattice of parallel conducting wires with finite length. We investigate a sub-wavelength focusing scheme with time reversal and demonstrate experimentally spots with focal widths of λ /25. Through a cross-correlation based imaging procedure we show an image reconstruction with a resolution of λ/80. Eventually we discuss the limitations of such a lens which reside essentially in losses. © 2011 Taylor & Francis. Mots-clés: Conducting wire; Cross correlations; Far-field; Far-field region; Finite length; MetaLens; Square lattices; Sub-diffraction; Sub-wavelength; Time reversal; Wire medium; Image reconstruction; Wire; Focusing
Synchronized passive imaging of single cavitation events Gateau, J., J.-F. Aubry, M. Pernota, D. Chauvet, A.-L. Boch, M. Fink, and M. Tanter AIP Conference Proceedings 1359, 79-84 (2011) Résumé: Passive cavitation detection techniques are usually of relatively low sensitivity to single cavitation events. Moreover, a single-element transducer is generally used, so that the spatial localization of these cavitation events is not possible, or is limited to the probing volume. To both detect and localize single cavitation events over an extended volume, the following experimental set-up has been used and validated: cavitation is induced with a focused single-element transducer (mean frequency 660kHz, f#=1) driven by a high power (up to 5kW) electric burst of a few cycles, and the acoustic emission of the bubbles is recorded on a standard linear array (4-7MHz), mounted on the side of the single element to probe its focal spot. Both the frequencies and the geometry used are appropriate to in vivo implementation. The recording of ultrasonic radio-frequency (RF) data was performed simultaneously on 64 channels of the array and was synchronized with the pulsed excitation. A single cavitation event results in a high frequency and coherent wave front on the RF data. Thanks to synchronization, these RF data are beam-formed to localize the event with a axial resolution of 0.3mm. A small number of discrete events could also be separated with this method. Besides, B-mode images obtained with the linear array prior to passive detection allowed the positioning of the events within the tissue structure. This technique has been used first ex vivo on freshly harve pig and sheep thigh muscle: with a two cycle excitation, a 9MPa cavitation threshold was found. Cavitation detection was also achieved in vivo with a five cycle burst excitation in sheep thigh muscle for a peak acoustic pressure of 11MPa. This technique could provide useful information in order to better understand, control and monitor the initiation phase of the histotripsy process © 2011 American Institute of Physics. Mots-clés: Passive detection; Single cavitation events
Transmission matrix in optics: Taking advantage of transmission channels for image transmission in disordered materials Popoff, S. M., G. Lerosey, R. Carminati, M. Fink, A. C. Boccara, and S. Gigan 2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference, CLEO EUROPE/EQEC 2011 (2011) Résumé: Recently, a method has been proposed by I. Vellekoop et al. [1] to focus light through a multiple scattering material, using a spatial light modulator as a tool to shape the incoming beam to obtain a maximal interference on a speckle spot of the output speckle pattern. The result is a bright, diffraction limited, spot which can be several hundred times brighter than the rest of the speckle. © 2011 IEEE. Mots-clés: Diffraction limited; Disordered materials; Spatial light modulators; Speckle patterns; Transmission channels; Transmission matrix; Electron optics; Light modulators; Optics; Quantum electronics; Speckle; Light
Noninvasive In Vivo Liver Fibrosis Evaluation Using Supersonic Shear Imaging: A Clinical Study on 113 Hepatitis C Virus Patients Bavu, É., J.-L. Gennisson, M. Couade, J. Bercoff, V. Mallet, M. Fink, A. Badel, A. Vallet-Pichard, B. Nalpas, M. Tanter, and S. Pol Ultrasound in Medicine and Biology 37, no. 9, 1361-1373 (2011) Résumé: Supersonic shear imaging (SSI) has recently been demonstrated to be a repeatable and reproducible transient bidimensional elastography technique. We report a prospective clinical evaluation of the performances of SSI for liver fibrosis evaluation in 113 patients with hepatitis C virus (HCV) and a comparison with FibroScan (FS). Liver elasticity values using SSI and FS ranged from 4.50 kPa to 33.96 kPa and from 2.60 kPa to 46.50 kPa, respectively. Analysis of variance (ANOVA) shows a good agreement between fibrosis staging and elasticity assessment using SSI and FS (p < 10 -5). The areas under receiver operating characteristic (ROC) curves for elasticity values assessed from SSI were 0.948, 0.962 and 0.968 for patients with predicted fibrosis levels F ≥ 2, F ≥ 3 and F = 4, respectively. These values are compared with FS area under the receiver operating characteristic curve (AUROC) of 0.846, 0.857 and 0.940, respectively. This comparison between ROC curves is particularly significant for mild and intermediate fibrosis levels. SSI appears to be a fast, simple and reliable method for noninvasive liver fibrosis evaluation. © 2011 World Federation for Ultrasound in Medicine & Biology. Mots-clés: 2-D transient elastography; Liver fibrosis staging; Shear wave imaging; Shear wave spectroscopy; Ultrasound; Clinical evaluation; Clinical study; Elasticity values; Elastography; Hepatitis C virus; In-vivo; Liver fibrosis; Liver fibrosis staging; Receiver operating characteristic curves; ROC curves; Shear wave imaging; Shear wave spectroscopy; Supersonic shear imaging; Transient elastography; Analysis of variance (ANOVA); Elasticity; Shear waves; Ultrasonic applications; Viruses; Shear flow; adu
Acoustic resonators for far-field control of sound on a subwavelength scale Lemoult, F., M. Fink, and G. Lerosey Physical Review Letters 107, no. 6 (2011) Résumé: We prove experimentally that broadband sounds can be controlled and focused at will on a subwavelength scale by using acoustic resonators. We demonstrate our approach in the audible range with soda cans, that is, Helmholtz resonators, and commercial computer speakers. We show that diffraction-limited sound fields convert efficiently into subdiffraction modes in the collection of cans that can be controlled coherently in order to obtain focal spots as thin as 1/25 of a wavelength in air. We establish that subwavelength acoustic pressure spots are responsible for a strong enhancement of the acoustic displacement at focus, which permits us to conclude with a visual experiment exemplifying the interest of our concept for subwavelength sensors and actuators. © 2011 American Physical Society. Mots-clés: Acoustic pressures; Diffraction limited; Far-field; Focal spot; Helmholtz resonators; Sensors and actuators; Strong enhancement; Sub-diffraction; Sub-wavelength; Subwavelength scale; Visual experiments; Acoustic fields; Resonators; Acoustic resonators
Functional ultrasound imaging of the brain Macé, E., G. Montaldo, I. Cohen, M. Baulac, M. Fink, and M. Tanter Nature Methods 8, no. 8, 662-664 (2011) Résumé: We present functional ultrasound (fUS), a method for imaging transient changes in blood volume in the whole brain at better spatiotemporal resolution than with other functional brain imaging modalities. fUS uses plane-wave illumination at high frame rate and can measure blood volumes in smaller vessels than previous ultrasound methods. fUS identifies regions of brain activation and was used to image whisker-evoked cortical and thalamic responses and the propagation of epileptiform seizures in the rat brain. © 2011 Nature America, Inc. All rights reserved. Mots-clés: animal experiment; animal model; article; blood volume; epileptic discharge; evoked cortical response; female; functional magnetic resonance imaging; functional ultrasound; illumination; imaging system; male; neuroimaging; nonhuman; priority journal; rat; thalamus; ultrasound; vibrissa; Algorithms; Animals; Brain; Brain Mapping; Evoked Potentials; Image Interpretation, Computer-Assisted; Rats; Ultrasonography; Rattus
Ultrafast imaging of the arterial pulse wave Couade, M., M. Pernot, E. Messas, J. Emmerich, A. Hagège, M. Fink, and M. Tanter IRBM 32, no. 2, 106-108 (2011) Résumé: We propose a novel technique for measuring directly in real time, locally and non-invasively the pulse wave velocity (PWV) on peripheral arteries. Very high frame rate ultrasonic imaging (> 1000 frames/s) was achieved for tracking in 2D the propagation of transient vibrations along arterial wall. The arterial pulse waves are observed within a single cardiac cycle allowing the estimation of the pulse wave velocity with a good accuracy. In this study, this technique was validated for PWV evaluation on 25 healthy patients using conventional sonographic probes. The mean carotid PWV was found to be 5.5 ± 1.2 m/s (from 4.5 m/s to 7 m/s) with good intra and interobserver variability (inferior of 10% of the mean). These data suggest a good accuracy and reproducibility of the technique for real time PWV evaluation in vitro and on healthy volunteers. © 2011 Elsevier Masson SAS. All rights reserved. Mots-clés: Arterial Stiffness; Pulse wave velocity (PWV); Ultrasound; Vascular imaging; artery diameter; artery wall; article; carotid artery; carotid artery pulse; common carotid artery; controlled study; heart cycle; human; human experiment; in vivo study; mechanical probe; normal human; pulse rate; pulse wave; ultrafast imaging scanner; ultrasound scanner; vibration
In vivo mapping of brain elasticity in small animals using shear wave imaging Macé, E., I. Cohen, G. Montaldo, R. Miles, M. Fink, and M. Tanter IEEE Transactions on Medical Imaging 30, no. 3, 550-558 (2011) Résumé: A combination of radiation force and ultrafast ultrasound imaging is used to both generate and track the propagation of a shear wave in the brain whose local speed is directly related to stiffness, characterized by the dynamic shear modulus G z.ast;. When performed on trepanated rats, this approach called shear wave imaging (SWI) provides 3-D brain elasticity maps reaching a spatial resolution of 0.7 mm × 1 mm × 0.4 mm with a good reproducibility (<13%). The dynamic shear modulus of brain tissues exhibits values in the 225 kPa range with a mean value of 12 kPa and is quantified for different anatomical regions. The anisotropy of the shear wave propagation is studied and the first in vivo anisotropy map of brain elasticity is provided. The propagation is found to be isotropic in three gray matter regions but highly anisotropic in two white matter regions. The good temporal resolution (∼ 10 ms per acquisition) of SWI also allows a dynamic estimation of brain elasticity to within a single cardiac cycle, showing that brain pulsatility does not transiently modify local elasticity. SWI proves its potential for the study of pathological modifications of brain elasticity both in small animal models and in clinical intra-operative imaging. © 2006 IEEE. Mots-clés: Anisotropy; brain; elasticity; shear wave imaging (SWI); ultrasound; Anatomical regions; Brain tissue; Cardiac cycles; Dynamic estimation; Dynamic shear modulus; Gray matter; In-vivo; Intra-operative; Local elasticity; Mean values; Pulsatility; Radiation forces; Reproducibilities; Shear wave imaging; shear wave imaging (SWI); Small Animal; Small animal model; Spatial resolution; Temporal resolution; Ultra-fast; ultrasound; Ultrasound imaging; White matter; Animals; Anisotropy; Brain models; Elas
Effects of nonlinear ultrasound propagation on high intensity brain therapy Pinton, G., J.-F. Aubry, M. Fink, and M. Tanter Medical Physics 38, no. 3, 1207-1216 (2011) Résumé: Purpose: As an ultrasound wave propagates nonlinearly, energy is transferred to higher frequencies where it is more strongly attenuated. Compared to soft tissue, the skull has strongly heterogeneous material parameters. The authors characterize with experiments and establish a numerical method that can describe the effects of the skull on the nonlinear components of ultrasonic wave propagation for application to high intensity focused ultrasound (HIFU) therapy in the brain. The impact of nonlinear acoustic propagation on heat deposition and thermal dose delivery is quantified and compared to linear assumptions by coupling an acoustic simulation with a heating model for brain tissue. Methods: A degassed dessicated human skull was placed in a water tank and insonified at 1 MPa with 7 mm transducer from a custom array designed for HIFU treatment. Two dimensional scans were performed preceding and following propagation through the skull with a calibrated hydrophone. Data from the scan preceding the skull were used as an input to a three dimensional finite difference time domain (FDTD) simulation that calculates the effects of diffraction, density, attenuation with linear dependence on frequency via relaxation mechanisms, and second order nonlinearity. A measured representation of the skull was used to determine the skull's acoustic properties. The validated acoustic model was used to determine the loss due to nonlinear propagation and then coupled to a finite difference simulation of the bioheat equation for two focal configurations at 3 and 7.5 cm from the skull surface. Results: Prior to propagation through the skull, the second harmonic component was 19 dB lower than the fundamental, and the third harmonic component was 37 dB lower. Following the skull, the second harmonic component was 35 dB lower and the third harmonic was 55 dB lower. The simulation is in agreement with the measurements to within 0.5 dB across the considered frequency range and shows good agreement across the two dimensional scan. It is then shown that the volume of treated brain is at least twice as large when assuming nonlinear acoustics. Conclusions: The authors have established a three dimensional FDTD simulation that accurately models the effects of nonlinearity and attenuation for propagation through the skull. Experimental validation shows good agreement across a broad frequency range and spatial extent. The nonlinear thermal dose was over an order of magnitude larger at the focus than the linear thermal dose and the necrotic volume was larger by at least a factor of 2. These results have particular applications to treatment planning. © 2011 American Association of Physicists in Medicine. Mots-clés: heating; nonlinear acoustics; ultrasound brain; article; biological model; body fluid; bone; brain; echography; heat; human; methodology; nonlinear system; reproducibility; statistical model; ultrasound; ultrasound therapy; Body Fluids; Bone and Bones; Brain; Hot Temperature; Humans; Linear Models; Models, Biological; Nonlinear Dynamics; Reproducibility of Results; Ultrasonic Therapy; Ultrasonics
Combined passive detection and ultrafast active imaging of cavitation events induced by short pulses of high-intensity ultrasound Gateau, J., J.-F. Aubry, M. Pernot, M. Fink, and M. Tanter IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 58, no. 3, 517-532 (2011) Résumé: The activation of natural gas nuclei to induce larger bubbles is possible using short ultrasonic excitations of high amplitude, and is required for ultrasound cavitation therapies. However, little is known about the distribution of nuclei in tissues. Therefore, the acoustic pressure level necessary to generate bubbles in a targeted zone and their exact location are currently difficult to predict. To monitor the initiation of cavitation activity, a novel all-ultrasound technique sensitive to single nucleation events is presented here. It is based on combined passive detection and ultrafast active imaging over a large volume using the same multi-element probe. Bubble nucleation was induced using a focused transducer (660 kHz, f-number = 1) driven by a high-power electric burst (up to 300 W) of one to two cycles. Detection was performed with a linear array (4 to 7 MHz) aligned with the single-element focal point. In vitro experiments in gelatin gel and muscular tissue are presented. The synchronized passive detection enabled radio-frequency data to be recorded, comprising highfrequency coherent wave fronts as signatures of the acoustic emissions linked to the activation of the nuclei. Active change detection images were obtained by subtracting echoes collected in the unnucleated medium. These indicated the appearance of stable cavitating regions. Because of the ultrafast frame rate, active detection occurred as quickly as 330 μs after the highamplitude excitation and the dynamics of the induced regions were studied individually. © 2011 IEEE. Mots-clés: Acoustics; Arrays; Heating; Imaging; Medical treatment; Transducers; Ultrasonic imaging; Acoustic pressure level; Active changes; Active detection; Active imaging; Arrays; Bubble nucleation; Cavitation activity; Cavitation events; Coherent wave front; Focal points; Focused transducer; Frame rate; High amplitudes; High frequency HF; High-power; Imaging; In-vitro; Linear arrays; Medical treatment; Multi-element; Muscular tissues; Passive detection; Radio-frequency datum; Short pulse; Ultra-fast; U
Time reversal of speckle noise Montaldo, G., M. Tanter, and M. Fink Physical Review Letters 106, no. 5 (2011) Résumé: Focusing a wave in an unknown inhomogeneous medium is an open problem in wave physics. This work presents an iterative method able to focus in pulse-echo mode in an inhomogeneous medium containing a random distribution of scatterers. By performing a coherent summation of the random echoes backscattered from a set of points surrounding the desired focus, a virtual bright pointlike reflector is generated. A time-reversal method enables an iterative convergence towards the optimal wave field focusing at the location of this virtual scatterer. Thanks to this iterative time-reversal process, it is possible to focus at any arbitrary point in the heterogeneous medium even in the absence of pointlike source. An experimental demonstration is given for the correction of strongly distorted images in the field of medical ultrasound imaging. This concept enables envisioning many other applications in wave physics. © 2011 American Physical Society. Mots-clés: Arbitrary points; Back-scattered; Coherent summation; Distorted images; Heterogeneous medium; Inhomogeneous medium; Medical ultrasound imaging; Open problems; Other applications; Pulse-echo mode; Random distribution; Speckle noise; Time-reversal; Time-reversal methods; Wavefields; Medical imaging
In Vivo quantitative mapping of myocardial stiffening and transmural anisotropy during the cardiac cycle Couade, M., M. Pernot, E. Messas, A. Bel, M. Ba, A. Hagege, M. Fink, and M. Tanter IEEE Transactions on Medical Imaging 30, no. 2, 295-305 (2011) Résumé: Shear wave imaging was evaluated for the in vivo assessment of myocardial biomechanical properties on ten open chest sheep. The use of dedicated ultrasonic sequences implemented on a very high frame rate ultrasonic scanner (>5000frames per second) enables the estimation of the quantitative shear modulus of myocardium several times during one cardiac cycle. A 128 element probe remotely generates a shear wave thanks to the radiation force induced by a focused ultrasonic burst. The resulting shear wave propagation is tracked using the same probe by cross-correlating successive ultrasonic images acquired at a very high frame rate. The shear wave speed estimated at each location in the ultrasonic image gives access to the local myocardial stiffness (shear modulus The technique was found to be reproducible (standard deviation hbox and able to estimate both systolic and diastolic stiffness on each sheep (respectively mu-diasapprox ≈2 kPa and μurm sysapprox ≈30kPa). Moreover, the ability of the proposed method to polarize the shear wave generation and propagation along a chosen axis permits the study the local elastic anisotropy of myocardial muscle. As expected, myocardial elastic anisotropy is found to vary with muscle depth. The real time capabilities and potential of Shear Wave Imaging using ultrafast scanners for cardiac applications is finally illustrated by studying the dynamics of this fractional anisotropy during the cardiac cycle. © 2010 IEEE. Mots-clés: Cardiac imaging; elastography; shear wave; ultrasound; Biomechanical properties; Cardiac applications; Cardiac cycles; Cardiac imaging; Elastic anisotropy; Elastography; Fractional Anisotropy; Frames per seconds; High frame rate; In-vivo; Quantitative mapping; Radiation forces; Real time capability; Shear modulus; Shear wave imaging; Shear wave speed; Standard deviation; Ultrafast scanners; Ultrasonic bursts; Ultrasonic images; Ultrasonic scanners; ultrasound; Wave generation; Anisotropy; Biomec
Ultrafast compound doppler imaging: Providing full blood flow characterization Bercoff, J., G. Montaldo, T. Loupas, D. Savery, F. Mézière, M. Fink, and M. Tanter IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 58, no. 1, 134-147 (2011) Résumé: Doppler-based flow analysis methods require acquisition of ultrasound data at high spatio-temporal sampling rates. These rates represent a major technical challenge for ultrasound systems because a compromise between spatial and temporal resolution must be made in conventional approaches. Consequently, ultrasound scanners can either provide full quantitative Doppler information on a limited sample volume (spectral Doppler), or averaged Doppler velocity and/or power estimation on a large region of interest (Doppler flow imaging). In this work, we investigate a different strategy for acquiring Doppler information that can overcome the limitations of the existing Doppler modes by significantly reducing the required acquisition time. This technique is called ultrafast compound Doppler imaging and is based on the following concept: instead of successively insonifying the medium with focused beams, several tilted plane waves are sent into the medium and the backscattered signals are coherently summed to produce highresolution ultrasound images. We demonstrate that this strategy allows reduction of the acquisition time by a factor of up to of 16 while keeping the same Doppler performance. Depending on the application, different directions to increase performance of Doppler analysis are proposed and the improvement is quantified: the ultrafast compound Doppler method allows faster acquisition frame rates for high-velocity flow imaging, or very high sensitivity for low-flow applications. Full quantitative Doppler flow analysis can be performed on a large region of interest, leading to much more information and improved functionality for the physician. By leveraging the recent emergence of ultrafast parallel beamforming systems, this paper demonstrates that breakthrough performances in flow analysis can be reached using this concept of ultrafast compound Doppler. © 2011 IEEE. Mots-clés: Acquisition time; Backscattered signal; Blood flow; Conventional approach; Doppler; Doppler analysis; Doppler flow imaging; Doppler imaging; Doppler information; Doppler methods; Doppler velocity; Flow analysis; Focused beams; Frame rate; High resolution; High sensitivity; High-velocity flows; Insonifying; Large regions; Parallel beamforming; Power estimations; Sample volume; Spatio-temporal; Technical challenges; Temporal resolution; Tilted planes; Ultra-fast; Ultrasound data; Ultrasound images
Image transmission through an opaque material Popoff, S., G. Lerosey, M. Fink, A. C. Boccara, and S. Gigan Nature Communications 1, no. 6 (2010) Résumé: Optical imaging relies on the ability to illuminate an object, collect and analyse the light it scatters or transmits. Propagation through complex media such as biological tissues was so far believed to degrade the attainable depth, as well as the resolution for imaging, because of multiple scattering. This is why such media are usually considered opaque. Recently, we demonstrated that it is possible to measure the complex mesoscopic optical transmission channels that allow light to traverse through such an opaque medium. Here, we show that we can optimally exploit those channels to coherently transmit and recover an arbitrary image with a high fidelity, independently of the complexity of the propagation. © 2010 Macmillan Publishers Limited. All rights reserved. Mots-clés: article; imaging system; laser diffraction; light scattering; optical tomography; visual system
Numerical prediction of frequency dependent 3D maps of mechanical index thresholds in ultrasonic brain therapy Pinton, G. F., J.-F. Aubry, M. Fink, and M. Tanter Proceedings - IEEE Ultrasonics Symposium, 2258-2261 (2010) Résumé: Therapeutic ultrasound has been used in brain therapy for thrombolysis and thermal ablation. Two approaches are used to transmit acoustic energy through the skull to the brain: low frequency ultrasound, with a wavelength that is larger than the skull thickness, and high frequency ultrasound, that is sensitive to aberrations and must use corrective techniques. At high frequency the Mechanical Index (MI) is lower, which translates to a higher cavitation threshold. The goal of this study is to determine if there is a comparable acoustic environment during high intensity focused ultrasound (HIFU) brain ablation at a high frequency by evaluating the volume that is above various MI thresholds for different device geometries that correspond to each treatment. The acoustic field was modeled with a 3D finite difference fullwave acoustic code developed by the authors that has been previously validated in a general acoustic context and with registered skull experiments. In addition to the non focused geometry of a 300 kHz blood clot treatment device two types of focused therapeutic transducers were modeled: a low frequency 300 kHz transducer, and a 1 MHz transducer that required aberration correction with a time reversal approach. It is shown that the brain volume above a range of MI is over three orders of magnitude larger at 300 kHz compared to 1 MHz. © 2010 IEEE. Mots-clés: Aberration correction; Acoustic energy; Acoustic environment; Blood clots; Brain therapy; Brain volume; Cavitation thresholds; Device geometries; Finite difference; High frequency; High frequency ultrasounds; High intensity focused ultrasound; Low frequency; Low-frequency ultrasound; Mechanical indexes; Mechanical indices; Numerical predictions; Therapeutic ultrasound; Thermal ablation; Three orders of magnitude; Thrombolysis; Time reversal; Ablation; Acoustic fields; Transducers; Ultrasonic tes
Detection and imaging of human beings behind a wall using the dort method Davy, M., T. Lepetit, J. De Rosny, C. Prada, and M. Fink Progress in Electromagnetics Research 110, 353-369 (2010) Résumé: In recent years, through the wall imaging has become a topic of intense research due to its promising applications in police, fire and rescue or emergency relief operations. In this paper, we propose to use the DORT method (French acronym for Decomposition of the Time Reversal Operator) to detect and localize a moving target behind a wall. One of the DORT method major strengths is that detection remains possible through a distorting medium. In this paper, the DORT method is successfully applied to detect and track moving human beings behind a thick concrete wall. The smallest detectable displacement is also investigated. Mots-clés: Concrete wall; Decomposition of the time reversal operator; Emergency relief; Human being; Moving targets; Through the wall imaging; Law enforcement; Walls (structural partitions)
Noninvasive assessment of myocardial anisotropy in vitro and in vivo using Supersonic Shear Wave Imaging Lee, W.-N., M. Couade, C. Flanagan, M. Fink, M. Pernot, and M. Tanter Proceedings - IEEE Ultrasonics Symposium, 690-693 (2010) Résumé: The knowledge of the myocardial fiber architecture is deemed essential and yet to be nondestructively investigated for myocardial mechanics and its association with the progression of myocardial diseases. In this study, Supersonic Shear Wave Imaging (SSI) was performed for its first time to noninvasively assess the fiber orientation (i.e., anisotropy) in in vitro porcine (N=5) and in vivo open-chest ovine (N=1) hearts. The SSI technique combined with the coherent plane-wave compounding method was performed to achieve both high echocardiographic image quality and ultrafast frame rate (8000 fps). An 8 MHz linear array probe (pitch =0.2 mm) was mounted on a customized rotation device, which allowed 360 rotation at 5° increments. The probe was initially aligned (±90° inclination) with the longitudinal axis in the local cardiac coordinates. The variation of the myocardial fiber orientation across the wall was observed in both in vitro and in vivo cases. Myocardial fibers were oriented gradually from the left diagonal (upper left to bottom right) near the epicardium (100% wall thickness) to the right diagonal (upper right to bottom left) near the endocardium with the midwall region dominated by the circumferential fibers. This finding was in good agreement with the literature and histology and has demonstrated the feasibility of SSI in mapping myocardial anisotropy. © 2010 IEEE. Mots-clés: anisotropy; fiber; myocardium; shear wave; supersonic; ultrafast; Echocardiographic images; Frame rate; In-vitro; In-vivo; Linear arrays; Longitudinal axis; Myocardial disease; Myocardial fiber architecture; myocardium; Non-invasive assessments; Plane wave; Shear wave imaging; supersonic; Ultra-fast; Wall thickness; Anisotropy; Echocardiography; Elasticity; Fibers; Heart; Image quality; Probes; Rotation; Shear waves; Ultrasonics; Shear flow
Adaptive focusing of transcranial therapeutic ultrasound using MR AcousticRadiation Force Imaging in a clinical environment Marsac, L., B. Larrat, M. Pernot, B. Robert, M. Fink, J.-F. Aubry, and M. Tanter Proceedings - IEEE Ultrasonics Symposium, 991-994 (2010) Résumé: Background: In order to focus ultrasound beams through aberrating layerssuch as fat or bones, adaptive focusing techniques have been proposed to improvethe focusing, mostly based on the backscattered echoes. We recently proposed anenergy-based technique with the sole requirement being knowledge of theacoustic intensity at the desired focus. Here, Magnetic Resonance- AcousticRadiation Force Imaging (MR-ARFI) is used to map the displacement induced by theradiation force of a focused ultrasound beam. As the maximum displacement isobtained with the best corrected beam, such a measurement can lead to aberrationcorrection. Material and methods: Proof of concept experiments were previouslyshown in a small animal MR at 7 T using a 64-elements linear phased arrayoperating at 6 MHz. Optimal refocusing was then obtained through numerical andphysical aberrating layers. This work is extended here in a clinical Philips 1.5T Achieva scanner. The HIFU beam is generated using a 512 elements US phasedarray (SuperSonic Imagine, France) dedicated to transcranial human experimentsand operating at 1 MHz. Experiments are conducted in phantom gels and ex vivobrain tissues through numerical phase aberrators. A motion-sensitized spin echosequence (TE 70 ms, TR 1200 ms, spatial resolution is 227 mm 3) isimplemented to measure displacements induced by the acoustic radiation force oftransmitted beams. Results: MR-ARFI allowed mapping the distribution of theradiation force at the focus of the array. After the recording of the MR phasesignals for different US emissions, the proposed adaptive focusing technique wasable to recover the spatial distribution of the phase aberrations. Totalacquisition time for 384 ultrasonic emission channels was 2 hours. Conclusion:Those first results in clinical MR at 1.5 T show that adaptive focusing of ahuman transcranial brain HIFU system can be achieved within reasonable timeunder MR guidance for aberrator layers as strong as human skull. Ongoing work isaiming at accelerating the acquisition in order to reach acceptable durationsfor in vivo protocols. © 2010 IEEE. Mots-clés: Acoustic Radiation Force Imaging; Adaptive focusing; brain; High Intensity FocusedUltrasound; MR guided therapy; Radiation Force; skull; Transcranial therapy; Acoustic Radiation Force Imaging; Adaptive focusing; High Intensity FocusedUltrasound; MR guided therapy; Radiation Force; skull; Transcranial; Acoustic emissions; Acoustic radiators; Acoustic wave propagation; Acoustic wave transmission; Experiments; Focusing; Tissue; Ultrasonic applications; Ultrasonics; Magnetic resonance
Evaluation of local arterial stiffness using ultrafast imaging: A comparative study using local arterial pulse wave velocity estimation and shear wave imaging Couade, M., C. Flanagan, W.-N. Lee, E. Messas, M. Fink, M. Pernot, and M. Tanter Proceedings - IEEE Ultrasonics Symposium, 475-478 (2010) Résumé: We have previously proposed a novel method for measuring arterial stiffness using shear wave imaging (SWI). In this study, we evaluate the performance of this method on a healthy population (N30) and we compare it to local measurement of the arterial pulse wave velocity (PWV) achieved at the same arterial site using ultrafast imaging. Ultrafast imaging was used to track shear wave induced remotely by acoustic radiation force at the carotid site at a frame rate of 10000 images/second with a 8 MHz ultrasound probe. SWI was acquired with a repetition rate of 7 Hz in order to measure stiffness variation over the cardiac cycle. The axial-velocity field in the imaging plane was obtained using conventional Doppler algorithm. As shown in a previous study, acoustic radiation force applied normally to the arterial wall induces mainly a flexural guided mode (F0) which propagates between 100 to 1500 Hz. The dispersion curve of this mode is extracted from the 2D-FFT of the shear wave spatio-temporal velocity field within and along the arterial wall. The shear modulus is then estimated by a theoretical fit of the experimental dispersion curve. Ultrafast imaging was also used to measure the tissue velocity of the arterial wall at the same site at a frame rate of 1000 images/s during 1 second. PWV was estimated by tracking the pulse wave along the arterial wall based on spatio-temporal velocity field at early and end-systole. Each ultrasound measurement was repeated 3 times on each carotid to estimate the reproducibility of the technique. Lower reproducibility was found on systolic PWV measurements. Thanks to its higher frequency content, the PWV at end-systole was measured more accurately and was found to be more reliable, but was not visible in all volunteers. In contrast, SWI offered high reproducibility. Moreover, arterial stiffness was achieved 6 times per seconds contrary to one time per second for PWV, giving access to the arterial stiffness time variation during the cardiac cycle. © 2010 IEEE. Mots-clés: Arterial stiffness; PWV; shear wave imaging; ultrafast imaging; A-frames; Acoustic radiation force; Arterial pulse; Arterial stiffness; Arterial wall; Cardiac cycles; Comparative studies; Dispersion curves; Doppler algorithms; Guided modes; Healthy population; High reproducibility; Higher frequencies; Imaging plane; Local measurement; Novel methods; Pulse wave; PWV; Repetition rate; Reproducibilities; shear wave imaging; Spatio-temporal; Stiffness variations; Time variations; ultrafast imaging;
Determination of the thickness - Plate velocity product of a plate structure with the green function comparison method Etaix, N., R.-K. Ing, A. Leblanc, and M. Fink 17th International Congress on Sound and Vibration 2010, ICSV 2010 3, 2246-2252 (2010) Résumé: Assuming the linearity of the Green's function with respect to the boundary conditions, it is demonstrated that the first antisymetric Lamb mode detected by a point receiver is proportional to that of a circular array of point receivers centred on it whatever location of the source and geometry of the plate. Therefore the Green function comparison method (GFCM) allows the determination of the plate velocity - thickness product from the measurement of ambient vibrations without using any emitter. Experimental results obtained with a plate of non regular geometry excited with a single transducer or a mobile loudspeaker kept in air are shown to validate theoretical approach. A second setup using a laser vibrometer to achieve the same measurements is realized for comparison purposes. Mots-clés: Ambient vibrations; Circular arrays; Comparison methods; Lamb modes; Laser vibrometers; Plate structure; Plate velocity; Regular geometry; Theoretical approach; Green's function; Vibrations (mechanical)
In vivo soft tissues elasticity during thermal therapy is linked to the thermal dose Sapin-Debrosses, E., M. Pernot, M. Fink, and M. Tanter Proceedings - IEEE Ultrasonics Symposium, 455-458 (2010) Résumé: Increasing interest is given to elasticity to monitor HIFU treatments, since elasticity changes during thermal ablation. Moreover, the shear modulus of in vitro soft tissue samples was proven to be linked to the thermal dose. Hence, the study aims to evaluate the link of in vivo elasticity changes, assessed by supersonic shear imaging, with temperature and thermal dose. Seven male rats (Sprague Dawley, 250 g) were anesthetized. The right leg was depilated and immersed in a thermo-regulated bath. Two optical temperature sensors were placed into the biceps femoris. The leg was warmed at a targeted temperature, from 38C to 50C, for a time corresponding to the theoretical threshold of necrosis in muscle (thermal dose 240 minutes at 43C). Every 40 seconds, shear plane waves were created in the biceps femoris, in a plane neighboring the thermocouples, using the Supersonic Shear Imaging method based on the radiation force. The shear wave propagation was acquired with 180 images at 10 000 frames/s. The changes of elasticity were assessed for the different temperature-time profiles in order to highlight its dependence with the thermal dose. The leg swelled when the temperature reached 39C. Then, contraction of the muscular fibers was observed on the Bmode images at 44-45C (thermal dose from 2 to 140 min), followed by a flow of fluid around the muscle. The effect of the thermal dose on the in vivo elasticity of the muscles was the same for all the rats. The shear modulus exponentially increased at a thermal dose was equal to 220 78 min. The cumulative thermal dose did not significantly change when the shear modulus reached 2.5 fold the initial value or more. Thus, this threshold value (220 min) was assumed to be the threshold of necrosis. This value is consistent with the necrosis of the skin and the theoretical threshold of necrosis of muscular tissues (240 min). This study gives promising prospects for the use of the elasticity to monitor thermal effects on tissues. © 2010 IEEE. Mots-clés: Acoustic Radiation Force; Shear Wave Imaging; Soft tissue elasticity; Thermal effects; Thermal Therapy; A-plane; A-thermal; Acoustic radiation force; B-mode images; Biceps femoris; In-vitro; In-vivo; Initial values; Male rats; Muscular tissues; Radiation forces; Shear plane; Shear Wave Imaging; Soft tissue; Soft tissue elasticity; Supersonic shear imaging; Temperature-time profiles; Thermal ablation; Thermal dose; Thermal therapies; Elastic moduli; Histology; Muscle; Rating; Rats; Shear flow; Sh
High sensitivity brain angiography using Ultrafast Doppler Macé, E., G. Montaldo, M. Fink, M. Tanter, I. Cohen, and R. Miles Proceedings - IEEE Ultrasonics Symposium, 1194-1197 (2010) Résumé: A new mode called Ultrafast Doppler based on the coherent compounding ofultrafast ultrasonic images is proposed for brain angiography. It is proved boththeoretically and experimentally on a trepanated rat that it increases by afactor 25 the sensitivity of Power Doppler images because both the number ofacquisitions for each pixel and the signal-to-noise ratio (SNR) are increasedwith Ultrafast Doppler. High quality images of the rat brain vascularization arepresented, showing the ability of Ultrafast Doppler to detect flows in verysmall vessels. In clinics, this technique could be applied for high qualitybrain angiography of newborn babies through the fontanel. © 2010 IEEE. Mots-clés: brain angiography; sensitivity; Ultrafast Doppler; Doppler; High quality images; High sensitivity; Power Doppler; Rat brain; sensitivity; Signal to noise; Ultra-fast; Ultrasonic images; Vascularization; Rats; Signal to noise ratio; Ultrasonic imaging; Ultrasonics; Angiography
In vivo study of cerebral ischemia using Shear Wave Imaging and Ultrafast Doppler Mace, E., G. Montaldo, M. Fink, M. Tanter, A. Martin, and B. Tavitian Proceedings - IEEE Ultrasonics Symposium, 1538-1541 (2010) Résumé: A multi-modal ultrasound imaging study of cerebral ischemia was performed on a rat model. Ischemia was obtained by the transient 2h occlusion of a cerebral artery and the lesion induced was imaged 1, 2, 4 and 7 days after the stroke. With Bmode imaging, the lesion was found to be hyperechogenic compared to normal brain tissue. With Shear Wave Imaging, the elasticity of the brain was measured showing that the ischemic lesion is softer than normal brain tissue and that its elasticity decreases significantly over time. With Ultrafast Doppler, the perfusion in the brain was measured showing that the lesion is hyperperfused compared to normal brain tissue with a peak two days after the occlusion. Ultrafast Doppler was also proved able to monitor the occlusion. Future work will focused on applying this multi-modal study for ischemic lesions induced by apoxia on newborn babies through the fontanel. © 2010 IEEE. Mots-clés: Cerebral ischemia; Shear Wave Imaging; Ultrafast Doppler; B-Mode imaging; Brain tissue; Cerebral arteries; Cerebral ischemia; Doppler; In-vivo; Multi-modal; Rat model; Shear Wave Imaging; Ultra-fast; Ultrafast Doppler; Ultrasound imaging; Brain; Elasticity; Shear waves; Tissue; Ultrasonic imaging; Ultrasonics; Shear flow
Comparison between 1D transient elastography and Supersonic Shear Imagingtechnique: Application to the arterial wall elasticity assessment Brum, J., N. Benech, C. Negreira, J.-L. Gennisson, M. Fink, and M. Tanter Proceedings - IEEE Ultrasonics Symposium, 1336-1339 (2010) Résumé: Early detection of biomechanical modifications in the arterial wall couldbe used as a predictor factor for various diseases, for example hypertension oratherosclerosis. In this work 1D transient elastography (TE) technique andSupersonic Shear Imaging (SSI) technique are used for the evaluation of theshear wave speed on a phantom consisting in 2.5 mm thickness viscoelastic layerand an arterial phantom embedded in gel. In the TE technique the polarization ofthe shear wave is parallel to its propagation and the true shear wave speed isretrieved. In that case the dispersion is mainly due to viscosity (Voigt'smodel). Regarding the SSI technique, the dispersion is due to the layerthickness being of the order of the shear wavelength: thus the shear wave isguided as a Lamb wave. In that case a model is needed in order to retrieve theshear wave speed from the dispersion curve. Finally through both techniquessimilar shear wave speed estimations are obtained. © 2010 IEEE. Mots-clés: arterial wall; elastography; shear wave propagation; Arterial wall; Dispersion curves; Early detection; Elastography; Lamb Wave; Shear wave speed; Shear wave speed estimation; Transient elastography; Wave speed; Biomechanics; Dispersion (waves); Elasticity; Shear waves; Ultrasonics; Wave propagation; Shear flow
Shear wave propagation in complex sub wavelength tissue geometries:Theoretical and experimental implications in the framework of cornea and skinshear wave imaging Nguyen, T.-M., J.-L. Gennisson, M. Couade, D. Touboul, P. Humbert, J. Bercoff, M. Fink, and M. Tanter Proceedings - IEEE Ultrasonics Symposium, 1145-1148 (2010) Résumé: Quantitative measurements of cornea and skin biomechanical properties havemany applications in medicine. In ophthalmology, it could lead to a betterdiagnosis of pathologies or monitoring of treatments. In dermatology, it couldhelp the skin lesions removal monitoring. In the framework of Supersonic ShearImaging (SSI), these organs are characterized by their complex sub wavelengthgeometry (thin plate and thin capsule) that strongly influences the shear wavepropagation. In this work, a theoretical framework is proposed and validated inexperiments for the quantification of elastic modulus in these layered tissues.Shear wave dispersion induced by the guided propagation in such thin layers isestimated and fitted to the analytical dispersion curve derived from the leakyLamb Wave theory. SSI is refined and used in order to map in real time thetissues elasticity. This technique consists in generating a shear wave byultrasonic radiation force and imaging its propagation through the medium at ahigh frame rate (20 kHz). For infinite media the shear wave velocity is thenlinked to the Young's modulus. In cornea and skin layers, the high-frequencyshear wave (from 500 to 2000 Hz) is guided similarly to a Lamb wave, with platethickness (<1 mm) close to its wavelength. Experimental dispersion curveshave been confronted to numerical studies. First, finite differences simulationswere performed to obtain numerical dispersion curves in plates with exactlyknown thickness and elasticity. Besides, theoretical dispersion equations werederived by solving numerically the propagation equation. Dispersion curvesobtained in vitro on phantoms are found consistent with analytical calculations.Least mean squares fitting of curves enables to recover a quantitativeassessment of elasticity (standard deviation <10%). © 2010 IEEE. Mots-clés: cornea stiffness; Lamb waves; shear wave dispersion; skinstiffness; supersonic shear imaging; cornea stiffness; Lamb Wave; shear wave dispersion; skinstiffness; Supersonic shear imaging; Biomechanics; Curve fitting; Dermatology; Dispersions; Elastic moduli; Elasticity; Monitoring; Shear flow; Shear waves; Tissue; Ultrasonic waves; Ultrasonics; Wave propagation; Dispersion (waves)
Measuring and exploiting the transmission matrix in optics Popoff, S. M., G. Lerosey, R. Carminati, M. Fink, A. C. Boceara, and S. Gigan Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference: 2010 Laser Science to Photonic Applications, CLEO/QELS 2010 (2010) Résumé: We introduce a method to measure the transmission matrix of a complex medium. This matrix exhibits statistical properties in good agreement with random matrix theory and allows light focusing and imaging through the random medium. ©2010 IEEE. Mots-clés: Complex medium; Light focusing; matrix; Random matrix theory; Random medium; Statistical properties; Transmission matrix
Quantitative Assessment of Arterial Wall Biomechanical Properties Using Shear Wave Imaging Couade, M., M. Pernot, C. Prada, E. Messas, J. Emmerich, P. Bruneval, A. Criton, M. Fink, and M. Tanter Ultrasound in Medicine and Biology 36, no. 10, 1662-1676 (2010) Résumé: A new ultrasound-based technique is proposed to assess the arterial stiffness: the radiation force of an ultrasonic beam focused on the arterial wall induces a transient shear wave (~10 ms) whose propagation is tracked by ultrafast imaging. The large and high-frequency content (100 to 1500 Hz) of the induced wave enables studying the wave dispersion, which is shown experimentally in vitro and numerically to be linked to arterial wall stiffness and geometry. The proposed method is applied in vivo. By repeating the acquisition up to 10 times per second (theoretical maximal frame rate is ~100 Hz), it is possible to assess in vivo the arterial wall elasticity dynamics: shear modulus of a healthy volunteer carotid wall is shown to vary strongly during the cardiac cycle and measured to be 130 ± 15 kPa in systole and 80 ± 10 kPa in diastole. (E-mail: ). © 2010 World Federation for Ultrasound in Medicine & Biology. Mots-clés: Acoustic radiation force; Arterial stiffness; Elastography; Ultrasound; Vascular imaging; Acoustic radiation force; Arterial stiffness; Elastography; Ultrasound; Vascular imaging; Acoustic emissions; Acoustic radiators; Acoustic wave propagation; Acoustic wave transmission; Biomechanics; Shear waves; Stiffness; Ultrasonic testing; Ultrasonics; Shear flow; adult; animal experiment; arterial stiffness; artery compliance; artery wall; article; biomechanics; carotid artery; diastole; echography; hea
Theory of electromagnetic time-reversal mirrors De Rosny, J., G. Lerosey, and M. Fink IEEE Transactions on Antennas and Propagation 58, no. 10, 3139-3149 (2010) Résumé: The theory of monochromatic time-reversal mirrors (TRM) or equivalently phase conjugate mirrors is developed for electromagnetic waves. We start from the fundamental time-symmetry of the Maxwell's equations. From this symmetry, a differential expression similar to the Lorentz reciprocity theorem is deduced. The radiating conditions on TRM are expressed in terms of 6-dimension Green's functions. To predict the time reversal focusing on antenna arrays, a formalism that involves impedance matrix is developed. We show that antenna coupling can dramatically modify the focal spot. Especially, we observe, that in some circumstances, sub-wavelength focusing on a bi-dimensional array may arise. © 2010 IEEE. Mots-clés: Antenna arrays; diffraction; microwaves; phase conjugate mirrors; plasmonic; sub-wavelength focusing; time-reversal; time-symmetry; Phase conjugate mirrors; Plasmonic; Sub-wavelength; Time-reversal; time-symmetry; Antenna phased arrays; Diffraction; Electromagnetic waves; Electromagnetism; Focusing; Green's function; Maxwell equations; Mirrors; Plasmons; Radio waves; Antennas
Real-time visualization of muscle stiffness distribution with ultrasound shear wave imaging during muscle contraction Shinohara, M., K. Sabra, J.-L. Gennisson, M. Fink, and M. L. Tanter Muscle and Nerve 42, no. 3, 438-441 (2010) Résumé: A stand-alone ultrasound shear wave imaging technology has been developed to quantify and visualize Young's modulus distribution by remotely applying ultrasound radiation force and tracking the resulting microvibrations in soft tissues with ultrafast ultrasound imaging. We report the first preliminary data that detected the distribution of local muscle stiffness within and between resting and contracting muscles at different muscle lengths with this technology. This technique may assist clinicians in characterizing muscle injuries or neuromuscular disorders. © 2010 Wiley Periodicals, Inc. Mots-clés: Dorsiflexion; Elastography; Plantarflexion; Spasticity; Young's modulus; adult; article; case report; echography; human; human experiment; male; muscle contraction; muscle length; muscle stiffness; normal human; priority journal; ultrasound; Young modulus; Adult; Biomechanics; Elasticity Imaging Techniques; Humans; Knee; Male; Muscle Contraction; Muscle, Skeletal; Physical Stimulation; Posture; Vibration
Ultrafast compound Doppler imaging: A new approach of Doppler flow analysis Montaldo, G., E. Macé, I. Cohen, J. Berckoff, M. Tanter, and M. Fink 2010 7th IEEE International Symposium on Biomedical Imaging: From Nano to Macro, ISBI 2010 - Proceedings, 324-327 (2010) Résumé: This work applies the concept of compounded plane wave transmissions at very high frames rates of some KHz for ultrafast Doppler analysis over a large region of interest. As this compound imaging method has a similar quality to the standard focusing method but is 10 times faster, it is possible to generate fast Doppler images at frame rates of 300Hz. This frame rate is able to visualize transient phenomena and to display duplex modes with simultaneous color and spectrum analysis for each pixel of the image. The interest of the method is not restricted to high velocity flows; by optimizing the quality of the ultrasonic compounded image, it is possible to image very small velocity flows. This method is applied to a functional imaging of the rat brain by detecting changes in the flow after a drug injection. ©2010 IEEE. Mots-clés: Brain imaging; Doppler; Ultrasound; Brain imaging; Compound imaging; Doppler; Doppler analysis; Doppler images; Doppler imaging; Doppler ultrasound; Drug injection; Duplex modes; Flow analysis; Frame rate; Functional imaging; High-velocity flows; Large regions; New approaches; Plane-wave transmission; Rat brain; Transient phenomenon; Ultra-fast; Velocity flow; Doppler effect; Medical imaging; Spectrum analysis; Spectrum analyzers; Ultrasonics
In vivo brain elasticity mapping in small animals using ultrasound and its application to cerebral ischemia Macé, E., I. Cohen, A. Martín, G. Montaldo, M. Fink, B. Tavitian, and M. Tanter 2010 7th IEEE International Symposium on Biomedical Imaging: From Nano to Macro, ISBI 2010 - Proceedings, 245-248 (2010) Résumé: Shear Wave Imaging (SWI) is an ultrasound based technique for elasticity imaging that has been successfully tested on several organs in the framework of cancer diagnosis. In this work, the potential of this technique to map brain elasticity in vivo on trepanned small animals is investigated. From a SWI scan of the rat brain, 3D elasticity maps are reconstructed reaching a spatial resolution of 800 μm. The dynamic modulus of the brain tissues exhibits values in the 1 to 16 kPa range and is quantified for different anatomical regions. The propagation of shear waves is found to be anisotropic, which could be a consequence of fiber orientation. Finally, the interest of brain elasticity mapping for the monitoring of brain ischemia is investigated on a rat model. Focal cerebral ischemia is shown to induce a dramatic decrease of elasticity in the lesion. ©2010 IEEE. Mots-clés: Brain elasticity; Cerebral ischemia; Shear wave imaging; Small animal; 3D elasticity; Anatomical regions; Brain ischemia; Brain tissue; Cancer diagnosis; Cerebral ischemia; Dynamic moduli; Elasticity imaging; Fiber orientations; In-vivo; Rat brain; Rat model; Shear wave imaging; Small Animal; Spatial resolution; Animals; Elasticity; Medical imaging; Shear flow; Shear waves; Three dimensional; Ultrasonic applications; Ultrasonics; Brain
Real time quantitative elastography using supersonic shear wave imaging Tanter, M., M. Pernot, G. Montaldo, J.-L. Gennisson, E. Bavu, E. Macé, T.-M. Nguyen, M. Couade, and M. Fink 2010 7th IEEE International Symposium on Biomedical Imaging: From Nano to Macro, ISBI 2010 - Proceedings, 276-279 (2010) Résumé: Supersonic Shear Imaging (SSI) is a quantitative stiffness imaging technique based on the combination of a radiation force induced in tissue by an ultrasonic beam and ultrafast ultrasound imaging sequence (up to more than 10000 frames per second) catching in real time the propagation of the resulting shear waves. Local shear wave speed is estimated and enables the two dimensional mapping of shear elasticity. This imaging modality is implemented on conventional probes driven by dedicated ultrafast echographic devices and can be performed during a standard ultrasound exam. The clinical potential of SSI is today extensively investigated for many potential applications such as breast cancer diagnosis, liver fibrosis staging, cardiovascular applications, ophthalmology. This invited lecture presents a short overview of the current investigated applications of SSI. ©2010 IEEE. Mots-clés: Cancer; Diagnosis; Elastography; Ultrafast imaging; Ultrasound; Breast cancer diagnosis; Cancer diagnosis; Cardiovascular applications; Elastography; Frames per seconds; Imaging modality; Liver fibrosis; Potential applications; Radiation forces; Real time; Shear elasticity; Shear wave imaging; Shear wave speed; Supersonic shear imaging; Two dimensional mapping; Ultra-fast; Ultrafast imaging; Ultrasonic beams; Ultrasound imaging; Medical imaging; Shear waves; Ultrasonic testing; Ultrasonics; Shea
MR-guided adaptive focusing of ultrasound Larrat, B., M. Pernot, G. Montaldo, M. Fink, and M. Tanter IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 57, no. 8, 1734-1747 (2010) Résumé: Adaptive focusing of ultrasonic waves under the guidance of a magnetic resonance (MR) system is demonstrated for medical applications. This technique is based on the maximization of the ultrasonic wave intensity at one targeted point in space. The wave intensity is indirectly estimated from the local tissue displacement induced at the chosen focus by the acoustic radiation force of ultrasonic beams. Coded ultrasonic waves are transmitted by an ultrasonic array and an MRI scanner is used to measure the resulting local displacements through a motion-sensitive MR sequence. After the transmission of a set of spatially encoded ultrasonic waves, a non-iterative inversion process is employed to accurately estimate the spatial-temporal aberration induced by the propagation medium and to maximize the acoustical intensity at the target. Both programmable and physical aberrating layers introducing strong distortions (up to 2π radians) were recovered within acceptable errors (<0.8 rad). This noninvasive technique is shown to accurately correct phase aberrations in a phantom gel with negligible heat deposition and limited acquisition time. These refocusing performances demonstrate a major potential in the field of MR-guided ultrasound therapy in particular for transcranial brain high-intensity focused ultrasound. © 2010 IEEE. Mots-clés: Acoustic radiation force; Acquisition time; Adaptive focusing; Heat deposition; High intensity focused ultrasound; Local displacement; MR sequence; MRI scanners; Non-iterative; Noninvasive technique; Phase aberrations; Spatial temporals; Tissue displacement; Transcranial; Ultrasonic arrays; Ultrasonic beams; Ultrasound therapy; Wave intensities; Aberrations; Acoustic fields; Gels; Geometrical optics; Medical applications; Resonance; Scanning; Ultrasonic testing; Ultrasonic waves; Ultrasonics
Thickness or phase velocity measurements using the Green's function comparison method Etaix, N., A. Leblanc, M. Fink, and R.-K. Ing IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 57, no. 8, 1804-1812 (2010) Résumé: The acoustic guided wave propagation for plate thickness measurement is generally treated in free space to simplify the formal approach. In this paper, propagation in a closed environment is treated by dealing with plates of finite dimensions and arbitrary geometries and linear boundary conditions. The present approach considers the plate Green's function to be composed of two terms. The first term corresponds to the Green's function of an infinite plate. The second term corresponds to a correction term which, in addition to the first term, satisfies all equations. Assuming the boundary conditions to be linear, it is found that the acoustic wave generated by a point source is proportional to that of a circular array of sources centered on it. By measuring the ratio between the two signals, either the plate velocity or plate thickness can be determined. This new method has been successfully applied to isotropic and anisotropic homogeneous plates of different geometries, on inhomogeneous plates, and also in a passive mode, without an active transmitter. © 2010 IEEE. Mots-clés: Arbitrary geometry; Circular arrays; Closed environment; Comparison methods; Different geometry; Finite dimensions; Formal approach; Free space; Guided wave propagation; Homogeneous plates; Infinite plate; Inhomogeneous plate; Passive mode; Plate thickness; Plate velocity; Point sources; Acoustic wave propagation; Acoustics; Boundary conditions; Guided electromagnetic wave propagation; Thickness measurement; Velocity measurement; Green's function
Breast lesions: Quantitative elastography with supersonic shear imaging - Preliminary results Athanasiou, A., A. Tardivon, M. Tanter, B. Sigal-Zafrani, J. Bercoff, T. Deffieux, J.-L. Gennisson, M. Fink, and S. Neuenschwander Radiology 256, no. 1, 297-303 (2010) Résumé: Purpose: To determine the appearance of breast lesions at quantitative ultrasonographic (US) elastography by using supersonic shear imaging (SSI) and to assess the correlation between quantitative values of lesion stiffness and pathologic results, which were used as the reference standard. Materials and Methods: This study was approved by the French National Committee for the Protection of Patients Participating in Biomedical Research Programs. All patients provided written informed consent. Conventional US and SSI quantitative elastography were performed in 46 women (mean age, 57.6 years;age range, 38-71 years) with 48 breast lesions (28 benign, 20 malignant;mean size, 14.7 mm);pathologic results were available in all cases. Quantitative lesion elasticity was measured in terms of the Young modulus (in kilopascals). Sensitivity, specifi city, and area under the curve were obtained by using a receiver operating characteristic curve analysis to assess diagnostic performance. Results: All breast lesions were detected at SSI. Malignant lesions exhibited a mean elasticity value of 146.6 kPa ± 40.05 (standard deviation), whereas benign ones had an elasticity value of 45.3 kPa ± 41.1 (P < .001). Complicated cysts were differentiated from solid lesions because they had elasticity values of 0 kPa (no signal was retrieved from liquid areas). Conclusion: SSI provides quantitative elasticity measurements, thus adding complementary information that potentially could help in breast lesion characterization with B-mode US. © RSNA, 2010. Mots-clés: adult; aged; article; B scan; breast biopsy; breast cancer; breast fibroadenoma; breast lesion; clinical article; controlled study; correlation analysis; diagnostic imaging; echomammography; elastography; female; fibrocystic breast disease; human; human tissue; image analysis; priority journal; quantitative diagnosis; sensitivity and specificity; Young modulus; Adult; Aged; Area Under Curve; Breast Neoplasms; Diagnosis, Differential; Elasticity Imaging Techniques; Female; Humans; Image Interpret
Measurement of thickness or plate velocity using ambient vibrations Ing, R. K., N. Etaix, A. Leblanc, and M. Fink Journal of the Acoustical Society of America 127, no. 6, EL252-EL257 (2010) Résumé: Assuming the Green's function is linear with respect to the boundary conditions, it is demonstrated that flexural waves detected by a point receiver and a circular array of point receivers centered on the previous receiver are proportional regardless location of the source and geometry of the plate. Therefore determination of plate velocity or thickness is done from the measurement of ambient vibrations without using any emitter. Experimental results obtained with a plate of non regular geometry excited with a single transducer or a remote loudspeaker are shown to verify the theoretical approach. © 2010 Acoustical Society of America. Mots-clés: Ambient vibrations; Circular arrays; Flexural wave; Plate velocity; Regular geometry; Theoretical approach; Electroacoustic transducers; Thickness measurement; Green's function
Resonant metalenses for breaking the diffraction barrier Lemoult, F., G. Lerosey, J. De Rosny, and M. Fink Physical Review Letters 104, no. 20 (2010) Résumé: We introduce the resonant metalens, a cluster of coupled subwavelength resonators. Dispersion allows the conversion of subwavelength wave fields into temporal signatures while the Purcell effect permits an efficient radiation of this information in the far field. The study of an array of resonant wires using microwaves provides a physical understanding of the underlying mechanism. We experimentally demonstrate imaging and focusing from the far field with resolutions far below the diffraction limit. This concept is realizable at any frequency where subwavelength resonators can be designed. © 2010 The American Physical Society. Mots-clés: Diffraction barrier; Diffraction limits; Far field; MetaLens; Purcell effect; Sub-wavelength; Sub-wavelength resonators; Temporal signatures; Underlying mechanism; Wavefields; Resonators
Spatio-temporal invariants of the time reversal operator Robert, J.-L., and M. Fink Journal of the Acoustical Society of America 127, no. 5, 2904-2912 (2010) Résumé: The decomposition of the time reversal operator, known by the French acronym DORT, is a technique to extract point scatterers monochromatic Greens functions from a medium. It is used to detect, locate, and focus on scatterers in various domains such as underwater acoustics, medical ultrasound, and nondestructive evaluation. A limitation of the method arises from its single-frequency nature, when the signals used in acoustics are often broadband. Reconstruction of the broadband Greens functions from the single-frequency Greens functions can be very difficult when numerous scatterers are present in the medium. Moreover, the method does not take advantage of the axial resolution associated with broadband signals. Time domain methods are investigated here as an answer to these problems. It is shown that the time reversal operator in the time domain takes the form of a tensor. The properties of the invariants are discussed. It is shown they do not have all the expected properties. Another method is proposed that requires a priori information on the medium. © 2010 Acoustical Society of America. Mots-clés: Axial resolutions; Broadband signal; Decomposition of the time reversal operator; Medical ultrasound; Non destructive evaluation; Priori information; Single-frequency; Spatio-temporal; Time domain; Time-domain methods; Time-reversal operator; Green's function; Scattering; Ultrasonic applications; Underwater acoustics; Time domain analysis; acoustics; algorithm; article; motion; radiation scattering; signal processing; sound; theoretical model; time; ultrasound; Acoustics; Algorithms; Models, The
Experimental validation of time reversal ultra wide-band communication system for high data rates Naqvi, I. H., G. E. Zein, G. Lerosey, J. De Rosny, P. Besnier, A. Tourin, and M. Fink IET Microwaves, Antennas and Propagation 4, no. 5, 643-650 (2010) Résumé: An experimental validation of high data rate communication for a time reversal (TR) ultra wide-band (UWB) communication system is performed using binary pulse amplitude modulation (BPAM) in two different dense multipath propagation channels for different data rates (15.62-Mbps≤Rb≤1-Gbps). From the measured received signals, signal, interference and noise contributions are separated. At very high data rates, interference has the most dominant contribution of all. Furthermore, without any processing and equalisation at the receiver, bit error rate (BER) performance is compared for different Rb It is shown that for Rb≤125-Mbps, TR system gives a good BER performance. Finally, the authors introduce a modified TR scheme in which total bandwidth of the TR system is divided into Nsub-bands contributing equal power in the power spectral density (PSD). This technique enables a flat PSD of the TR transmitted signal, reduces inter symbol interference (ISI) and therefore improves the BER performance of the system. © 2010 © The Institution of Engineering and Technology. Mots-clés: BER performance; Bit error rate performance; Data rates; Dense multipath; Dominant contributions; Equalisation; Experimental validations; High data rate; High data rate communications; Noise contributions; Propagation channels; Received signals; Time reversal; Transmitted signal; Ultra-wideband communications; Amplitude modulation; Broadband networks; Communication systems; Data flow analysis; Power spectral density; Pulse amplitude modulation; Satellite communication systems; Bit error rate
Imaging: Sharper focus by random scattering Fink, M. Nature Photonics 4, no. 5, 269-271 (2010)
High intensity focused ultrasound for transcranial therapy of brain lesions and disorders Aubry, J.-F., L. Marsac, M. Pernot, B. Robert, A.-L. Boch, D. Chauvet, N. Salameh, L. Souris, L. Darasse, J. Bittoun, Y. Martin, C. Cohen-Bacrie, J. Souquet, M. Fink, and M. Tanter IRBM 31, no. 2, 87-91 (2010) Résumé: A novel MR-guided brain therapy device operating at 1 MHz has been designed and constructed. The system has been installed and tested in a clinical 1.5 T Philips Achieva MRI. Skull bone distortions induced on the ultrasonic beam are corrected using the concept of time reversal focusing. Prior to the treatment, a 3D CT scan of the patient head is performed and used as entry parameters for three-dimensional finite differences simulations that compute the propagation of the wave field through the human skull. The simulated phase distortions are then used as inputs for transcranial corrections. Temperature elevations during the treatment are imaged using MRI thermometry thus ensuring the control and safety of this therapeutic approach. First experiments are performed on four human cadavers and the promising results allow us to envision a first clinical investigation of this therapeutic approach in a near future. First targeted applications correspond to the non-invasive treatment of brain metastases and neurologic disorders such as the essential tremor. © 2010. Mots-clés: Brain; Cancer; Focalisation; MRI; Therapy; Thermal ablation; Thermometry; Ultrasound; article; brain damage; brain disease; cadaver; computer assisted tomography; equipment design; high intensity focused ultrasound; human; image processing; image reconstruction; nuclear magnetic resonance imaging; parameter; safety; simulation; skull; thermometry; three dimensional imaging
Viscoelastic and anisotropic mechanical properties of in vivo muscle tissue assessed by supersonic shear imaging Gennisson, J.-L., T. Deffieux, E. Macé, G. Montaldo, M. Fink, and M. Tanter Ultrasound in Medicine and Biology 36, no. 5, 789-801 (2010) Résumé: The in vivo assessment of the biomechanical properties of the skeletal muscle is a complex issue because the muscle is an anisotropic, viscoelastic and dynamic medium. In this article, these mechanical properties are characterized for the brachialis muscle in vivo using a noninvasive ultrasound-based technique. This supersonic shear imaging technique combines an ultra-fast ultrasonic system and the remote generation of transient mechanical forces into tissue via the radiation force of focused ultrasonic beams. Such an ultrasonic radiation force is induced deep within the muscle by a conventional ultrasonic probe and the resulting shear waves are then imaged with the same probe (5 MHz) at an ultra-fast framerate (up to 5000 frames/s). Local tissue velocity maps are obtained with a conventional speckle tracking technique and provide a full movie of the shear wave propagation through the entire muscle. Shear wave group velocities are then estimated using a time of flight algorithm. This approach provides a complete set of quantitative and in vivo parameters describing the muscle's mechanical properties as a function of active voluntary contraction as well as passive extension of healthy volunteers. Anisotropic properties are also estimated by tilting the probe head with respects to the main muscular fibers direction. Finally, the dispersion of the shear waves is studied for these different configurations and shear modulus and shear viscosity are quantitatively assessed assuming the viscoelastic Voigt's model. © 2010 World Federation for Ultrasound in Medicine & Biology. Mots-clés: Anisotropy; Muscle tissue; Supersonic shear imaging; Transient elastography; Viscoelastic; Anisotropic mechanical properties; Anisotropic property; Biomechanical properties; Frame-rate; In-vivo; Muscle tissues; Radiation forces; Shear modulus; Skeletal muscle; Speckle tracking technique; Supersonic shear imaging; Time of flight; Transient elastography; Transient mechanical; Ultra-fast; Ultrasonic beams; Ultrasonic probe; Ultrasonic radiation force; Ultrasonic system; Velocity maps; Voluntary con
Experimental study of the invariants of the time-reversal operator for a dielectric cylinder using separate transmit and receive arrays Davy, M., J.-G. Minonzio, J. De Rosny, C. Prada, and M. Fink IEEE Transactions on Antennas and Propagation 58, no. 4, 1349-1356 (2010) Résumé: The decomposition of the time reversal operator (DORT method) is applied to electromagnetic waves in order to characterize a dielectric cylinder. It consists in determining the Time Reversal Invariants of the Time Reversal Operator. Here, this matrix is built from the inter-element responses between distinct transmit and receive arrays. In this paper experimental results obtained between 2 and 4 GHz are compared to a theoretical model, developed in an other paper (Minonzio , Theory of the time-reversal operator for a dielectric cylinder using separate transmit and receive arrays, IEEE Trans. Antennas Propag., vol. 57, pp. 23312340, 2009). The DORT method is then applied to an inverse problem to determine the diameter and the permittivity of the cylinder. It is shown experimentally that different experimental parameters can be estimated from the singular values of the time reversal operator. © 2006 IEEE. Mots-clés: Antenna array processing; Electromagnetic inverse problem; Electromagnetic scattering; Decomposition of the time reversal operator; Dielectric cylinder; Electromagnetic inverse problems; Electromagnetic scattering; Experimental parameters; Experimental studies; matrix; Singular values; Theoretical models; Time reversal; Time-reversal operator; Antenna arrays; Array processing; Cylinders (shapes); Dielectric devices; Electromagnetic wave scattering; Electromagnetic waves; Inverse problems; Microw
Non invasive transcostal focusing based on the decomposition of the time reversal operator: In vitro validation Cochard, É., C. Prada, J.-F. Aubry, and M. Fink AIP Conference Proceedings 1215, 131-135 (2010) Résumé: Thermal ablation induced by high intensity focused ultrasound has produced promising clinical results to treat hepatocarcinoma and other liver tumors. However skin burns have been reported due to the high absorption of ultrasonic energy by the ribs. This study proposes a method to produce an acoustic field focusing on a chosen target while sparing the ribs, using the decomposition of the time-reversal operator (DORT method). The idea is to apply an excitation weight vector to the transducers array which is orthogonal to the subspace of emissions focusing on the ribs. The ratio of the energies absorbed at the focal point and on the ribs has been enhanced up to 100-fold as demonstrated by the measured specific absorption rates. © 2010 American Institute of Physics. Mots-clés: Adaptive focusing; DORT; High intensity focused ultrasound; Noninvasive surgery; Phased array
MR-guided ultrasonic brain therapy: High frequency approach Aubry, J. F., L. Marsac, M. Pernot, M. Tanter, B. Robert, M. Brentnall, P. Annic, R. La Greca, A. De Charentenay, F. Pomatta, Y. Martin, C. Cohen-Bacrie, J. Souquet, and M. Fink AIP Conference Proceedings 1215, 88-94 (2010) Résumé: A novel MR-guided brain therapy device operating at 1 MHz has been designed and constructed. The system has been installed and tested in a clinical 1.5 T Philips Achieva MRI. Three dimensional time domain finite differences simulations were used to compute the propagation of the wave field through three human skulls. The simulated phase distortions were used as inputs for transcranial correction and the corresponding pressure fields were scanned in the focal plane. At half of the maximum power (10W/cm2 on the surface of the transducers), necroses were induced 2 cm deep in turkey breasts placed behind a human skull. In vitro experiments on human skulls show that simulations restore more than 85% of the pressure level through the skull bone when compared to a control correction performed with an implanted hydrophone. Finally, high power experiments are performed though the skull bone and a MR-Thermometry sequence is used to map the temperature rise in a brain phantom every 3 s in two orthogonal planes (focal plane and along the axis of the probe). © 2010 American Institute of Physics. Mots-clés: HIFU; MR guided therapy; Transcranial therapy
MR guidance, monitoring and control of brain HIFU therapy in small animals: In vivo demonstration in rats Larrat, B., M. Pernot, E. Dervishi, A. Souilah, D. Seilhean, Y. Marie, A. L. Boch, J. F. Aubry, M. Fink, and M. Tanter AIP Conference Proceedings 1215, 105-109 (2010) Résumé: In the framework of HIFU transcranial brain therapy, it is mandatory to develop techniques capable of assessing the focusing quality and location before the treatment. Monitoring heat deposition in real time and verifying the extension of the treated area are also important steps. In this study, an imaging protocol is proposed to:1/ locate the US radiation force induced displacement in tissues and quantify the acoustic pressure at focus prior to HIFU; 2/ monitor the temperature rise during HIFU; and 3/ assess the changes in elasticity in the treated area. A 7T MRI scanner was equipped with a home-made stereotactic frame for rats and a US focused transducer working at 1.5 MHz. Such a tool is key for the evaluation of the biological effects of HIFU on brain tissue and tumors. The proposed protocol was successfully tested on 12 rats with and without injected tumors. The accurate localization of the focal point prior to HIFU was demonstrated in vivo. Furthermore, the pressure estimation in situ allowed to accurately simulate the heat deposition at focus and to plan the treatment (electrical power, duration). The temperature measurements were in good accordance with the predicted curves. The elasticity maps showed significant changes after treatment in some cases. © 2010 American Institute of Physics. Mots-clés: Brain; High intensity focused ultrasound; Magnetic resonance elastography; Magnetic resonance thermometry; Monitoring; Radiation force localization; Rat; Transcranial
Energy-based adaptive focusing: Optimal ultrasonic focusing using magnetic resonance guidance Larrat, B., M. Pernot, G. Montaldo, M. Fink, and M. Tanter AIP Conference Proceedings 1215, 140-144 (2010) Résumé: Adaptive focusing of ultrasonic waves is performed under the guidance of a Magnetic Resonance (MR) system. The technique is based on the maximization of the ultrasonic wave intensity at a target point. The wave intensity is indirectly estimated from the local tissue motion induced at the chosen focus by the acoustic radiation force of the ultrasonic beam. A motion sensitive MR sequence is used to measure the resulting local tissue displacements. Based on the transmission of a set of spatially coded ultrasonic waves, a non iterative inversion process is used to estimate the phase aberrations induced by the propagation medium and to maximize the acoustical intensity at the target. Both programmable and physical aberrating layers introducing strong distortions (up to 2π radians) are recovered within acceptable errors (<0.8 rad). This non invasive technique is shown to accurately correct the phase aberrations in a phantom gel with negligible heat deposition and limited acquisition time. These refocusing performances demonstrate a major potential in the field of MR-Guided Ultrasound Therapy in particular for transcranial brain HIFU. © 2010 American Institute of Physics. Mots-clés: Acoustic radiation force; Adaptive focusing; HIFU; MR guided therapy; Transcranial therapy
Temperature dependence of the shear modulus of soft tissues assessed by ultrasound Sapin-De Brosses, E., J.-L. Gennisson, M. Pernot, M. Fink, and M. Tanter Physics in Medicine and Biology 55, no. 6, 1701-1718 (2010) Résumé: Soft tissue stiffness was shown to significantly change after thermal ablation. To better understand this phenomenon, the study aims (1) to quantify and explain the temperature dependence of soft tissue stiffness for different organs, (2) to investigate the potential relationship between stiffness changes and thermal dose and (3) to study the reversibility or irreversibility of stiffness changes. Ex vivo bovine liver and muscle samples (N = 3 and N = 20, respectively) were slowly heated and cooled down into a thermally controlled saline bath. Temperatures were assessed by thermocouples. Sample stiffness (shear modulus) was provided by the quantitative supersonic shear imaging technique. Changes in liver stiffness are observed only after 45 °C. In contrast, between 25 °C and 65 °C, muscle stiffness varies in four successive steps that are consistent with the thermally induced proteins denaturation reported in the literature. After a 6 h long heating and cooling process, the final muscle stiffness can be either smaller or bigger than the initial one, depending on the stiffness at the end of the heating. Another important result is that stiffness changes are linked to thermal dose. Given the high sensitivity of ultrasound to protein denaturation, this study gives promising prospects for the development of ultrasound-guided HIFU systems. © 2010 Institute of Physics and Engineering in Medicine. Mots-clés: Bovine liver; Cooling process; Ex-vivo; High sensitivity; Liver stiffness; Muscle stiffness; Protein denaturation; Shear modulus; Soft tissue; Supersonic shear imaging; Temperature dependence; Thermal ablation; Thermal dose; Thermally induced; Coagulation; Elastic moduli; Heating; Imaging techniques; Liver; Muscle; Proteins; Temperature distribution; Thermocouples; Ultrasonic applications; Ultrasonics; Stiffness
Measuring the transmission matrix in optics: An approach to the study and control of light propagation in disordered media Popoff, S. M., G. Lerosey, R. Carminati, M. Fink, A. C. Boccara, and S. Gigan Physical Review Letters 104, no. 10 (2010) Résumé: We introduce a method to experimentally measure the monochromatic transmission matrix of a complex medium in optics. This method is based on a spatial phase modulator together with a full-field interferometric measurement on a camera. We determine the transmission matrix of a thick random scattering sample. We show that this matrix exhibits statistical properties in good agreement with random matrix theory and allows light focusing and imaging through the random medium. This method might give important insight into the mesoscopic properties of a complex medium. © 2010 The American Physical Society. Mots-clés: Complex medium; Disordered media; Full-field; Interferometric measurement; matrix; Mesoscopic properties; Random matrix theory; Random medium; Random scattering; Spatial phase modulator; Statistical properties; Transmission matrix; Light; Light propagation; Light transmission
Multiwave imaging and super resolution Fink, M., and M. Tanter Physics Today 63, no. 2, 28-33 (2010) Résumé: The human body supports the propagation of many kinds of waves, each of which can provide an image with a specific type of information. For example, ultrasonic waves reveal a tissue's density and how it responds to compression forces, and mechanical shear waves indicate how tissues respond to shear forces. Low-frequency electromagnetic waves are sensitive to electrical conductivity; optical waves tell about optical absorption. In all those circumstances, physicists have striven to obtain the best overall contrast and resolution. Now, after decades of work, we are pushing against the physical limits inherent in each imaging modality. As described in the box on page 30, that limit is, in many cases, not determined by wavelength. © 2010 American Institute of Physics.
MR-guided transcranial brain HIFU in small animal models Larrat, B., M. Pernot, J.-F. Aubry, E. Dervishi, R. Sinkus, D. Seilhean, Y. Marie, A.-L. Boch, M. Fink, and M. Tanter Physics in Medicine and Biology 55, no. 2, 365-388 (2010) Résumé: Recent studies have demonstrated the feasibility of transcranial high-intensity focused ultrasound (HIFU) therapy in the brain using adaptive focusing techniques. However, the complexity of the procedures imposes provision of accurate targeting, monitoring and control of this emerging therapeutic modality in order to ensure the safety of the treatment and avoid potential damaging effects of ultrasound on healthy tissues. For these purposes, a complete workflow and setup for HIFU treatment under magnetic resonance (MR) guidance is proposed and implemented in rats. For the first time, tissue displacements induced by the acoustic radiation force are detected in vivo in brain tissues and measured quantitatively using motion-sensitive MR sequences. Such a valuable target control prior to treatment assesses the quality of the focusing pattern in situ and enables us to estimate the acoustic intensity at focus. This MR-acoustic radiation force imaging is then correlated with conventional MR-thermometry sequences which are used to follow the temperature changes during the HIFU therapeutic session. Last, pre- and post-treatment magnetic resonance elastography (MRE) datasets are acquired and evaluated as a new potential way to non-invasively control the stiffness changes due to the presence of thermal necrosis. As a proof of concept, MR-guided HIFU is performed in vitro in turkey breast samples and in vivo in transcranial rat brain experiments. The experiments are conducted using a dedicated MR-compatible HIFU setup in a high-field MRI scanner (7 T). Results obtained on rats confirmed that both the MR localization of the US focal point and the pre- and post-HIFU measurement of the tissue stiffness, together with temperature control during HIFU are feasible and valuable techniques for efficient monitoring of HIFU in the brain. Brain elasticity appears to be more sensitive to the presence of oedema than to tissue necrosis. © 2010 Institute of Physics and Engineering in Medicine. Mots-clés: Acoustic radiation force; Adaptive focusing; Brain tissue; Damaging effects; Data sets; Efficient monitoring; Focal points; Healthy tissues; High field MRI; High intensity focused ultrasound; In-situ; In-vitro; In-vivo; Magnetic resonance elastography; Magnetic resonance guidances; Monitoring and control; MR sequence; MR-compatible; MR-thermometry; Post treatment; Proof of concept; Rat brain; Small animal model; Temperature changes; Therapeutic modality; Thermal necrosis; Tissue displacement; Ti
Focusing and amplification of electromagnetic waves by time reversal in an leaky reverberation chamber Davy, M., J. De Rosny, J.-C. Joly, and M. Fink Comptes Rendus Physique 11, no. 1, 37-43 (2010) Résumé: In this article, time reversal is used to generate high power microwave pulses from a low power arbitrary wave generator. We use a reverberation chamber with an aperture on the front face and we take advantage of the pulse compression property of time reversal. High amplitude peaks are generated outside the chamber thanks to the long spreading time of the signals inside. We study the amplitude of this peak and the width of the focal spot with respect to the different experimental parameters. A gain of 18 dB compared to a directive antenna of the same aperture is obtained. © 2010 Académie des sciences. Mots-clés: Focal spot; Gain; Reverberation cavity; Time reversal
Transcranial ultrasonic therapy based on time reversal of acoustically induced cavitation bubble signature Gâteau, J., L. Marsac, M. Pernot, J.-F. Aubry, M. Tanter, and M. Fink IEEE Transactions on Biomedical Engineering 57, no. 1, 134-144 (2010) Résumé: Brain treatment through the skull with high-intensity focused ultrasound can be achieved with multichannel arrays and adaptive focusing techniques such as time reversal. This method requires a reference signal to be either emitted by a real source embedded in brain tissues or computed from a virtual source, using the acoustic properties of the skull derived from computed tomography images. This noninvasive computational method focuses with precision, but suffers from modeling and repositioning errors that reduce the accessible acoustic pressure at the focus in comparison with fully experimental time reversal using an implanted hydrophone. In this paper, this simulation-based targeting has been used experimentally as a first step for focusing through an ex vivo human skull at a single location. It has enabled the creation of a cavitation bubble at focus that spontaneously emitted an ultrasonic wave received by the array. This active source signal has allowed 97 ± 1.1 of the reference pressure (hydrophone-based) to be restored at the geometrical focus. To target points around the focus with an optimal pressure level, conventional electronic steering from the initial focus has been combined with bubble generation. Thanks to step-by-step bubble generation, the electronic steering capabilities of the array through the skull were improved. © 2009 IEEE. Mots-clés: Acoustic beam steering; Acoustic cavitation; Adaptive arrays; Transcranial brain therapy; Acoustic beams; Acoustic cavitations; Adaptive arrays; Brain therapy; Transcranial; Acoustic properties; Acoustic waves; Computerized tomography; Hydrophones; Military photography; Quantum theory; Ultrasonics; Cavitation; acoustic cavitation; acoustics; article; computer assisted tomography; gold standard; high intensity focused ultrasound; mathematical model; microbubble; phantom; skull; transcranial ultra
Influence of noise on subwavelength imaging of two close scatterers using time reversal method: Theory and experiments Davy, M., J.-G. Minonzio, J. De Rosny, C. Prada, and M. Fink Progress in Electromagnetics Research 98, 333-358 (2009) Résumé: Although classical imaging is limited by the Rayleigh criterion, it has been demonstrated that subwavelength imaging of two point-like scatterers can be achieved with probing sensors arrays, even if the scatterers are located in the far field of the sensors. However, the role of noise is crucial to determine the resolution limit. This paper proposes a quantitative study of the influence of noise on the subwavelength resolution obtained with the DORT-MUSIC method. The DORT method, French acronym for decomposition of the time reversal operator, consists in studying the invariants of the time reversal operator. The method is combined here with the estimator MUSIC (MUltiple SIgnal Classification) to detect and image two close metallic wires. The microwaves measurements are performed between 2.6GHz and 4GHz. Two wires of λ/100 diameters separated by λ/6 are imaged and separated experimentally. To interpret this result in terms of noise level, the analytical expression of the eigenvectors of the time reversal operator perturbed by the noise is established. We then deduce the noise level above which the subwavelength resolution fails. Numerical simulations and experimental results validate the theoretical developments. Mots-clés: Analytical expressions; Classical imaging; Decomposition of the time reversal operator; Eigenvectors; Far field; Metallic wire; Multiple signal classification; Music method; Noise levels; Numerical simulation; Quantitative study; Rayleigh criterion; Resolution limits; Sensors array; Subwavelength imaging; Subwavelength resolution; Theoretical development; Time-reversal methods; Time-reversal operator; Two-point; Computer simulation; Scattering; Sensor arrays; Wavelet analysis; Wire; Quantum theo
Energy-based adaptive focusing: Optimal ultrasonic focusing using magnetic resonance guidance Larrat, B., M. Pernot, G. Montaldo, M. Fink, and M. Tanter Proceedings - IEEE Ultrasonics Symposium (2009) Résumé: Adaptive focusing of ultrasonic waves is performed under the guidance of a Magnetic Resonance (MR) system. The technique is based on the maximization of the ultrasonic wave intensity at a target point. The wave intensity is indirectly estimated from the local tissue motion induced at the chosen focus by the acoustic radiation force of the ultrasonic beam. A motion sensitive MR sequence is used to measure the resulting local tissue displacements. Based on the transmission of a set of spatially coded ultrasonic waves, a non iterative inversion process is used to estimate the phase aberrations induced by the propagation medium and to maximize the acoustical intensity at the target. Both programmable and physical aberrating layers introducing strong distortions (up to 2π radians) are recovered within acceptable errors (<0.8 rad). This non invasive technique is shown to accurately correct the phase aberrations in a phantom gel with negligible heat deposition and limited acquisition time. These refocusing performances demonstrate a major potential in the field of MR-Guided Ultrasound Therapy in particular for transcranial brain HIFU. ©2009 IEEE. Mots-clés: Acoustic radiation force; Adaptive focusing; HIFU; MR guided therapy; Transcranial therapy; Acoustic radiation force; Acquisition time; Adaptive focusing; Heat deposition; Magnetic resonance guidances; MR sequence; Non-iterative; Noninvasive technique; Phase aberrations; Target point; Tissue displacement; Tissue motion; Transcranial; Ultrasonic beams; Ultrasonic focusing; Ultrasound therapy; Wave intensities; Aberrations; Acoustic emissions; Acoustic fields; Acoustic radiators; Acoustic wave pro
High-resolution quantitative imaging of cornea elasticity using supersonic shear imaging Tanter, M., D. Touboul, J.-L. Gennisson, J. Bercoff, and M. Fink IEEE Transactions on Medical Imaging 28, no. 12, 1881-1893 (2009) Résumé: The noninvasive estimation of in vivo mechanical properties of cornea is envisioned to find several applications in ophthalmology. Such high-resolution measurements of local cornea stiffness could lead to a better anticipation and understanding of corneal pathologies such as Keratoconus. It could also provide a quantitative evaluation of corneal biomechanical response after corneal refractive surgeries and a tool for evaluating the efficacy of new cornea treatments such as cornea transplant using femtosecond laser or therapy based on Riboflavin/UltraViolet-A Corneal Cross Linking (UVA CXL). In the very important issue of glaucoma diagnosis and management, the fine tuning corneal elasticity measurement could also succeed to strongly correlate the applanation tonometry with the true intra-ocular pressure (IOP). This initial investigation evaluates the ability of ultrafast and high-resolution ultrasonic systems to provide a real-time and quantitative mapping of corneal viscoelasticity. Quantitative elasticity maps were acquired ex vivo on porcine cornea using the supersonic shear imaging (SSI) technique. A conventional 15 MHz linear probe was used to perform conventional ultrasonic imaging of the cornea. A dedicated ultrasonic sequence combines the generation of a remote palpation in the cornea and ultrafast (20000 frames/s) ultrasonic imaging of the resulting corneal displacements that evolve into a shear wave propagation whose local speed was directly linked to local elasticity. A quantitative high-resolution map (150 mum resolution) of local corneal elasticity can be provided by this dedicated sequence of ultrasonic insonifications. Quantitative maps of corneal elasticity were obtained on ex vivo freshly enucleated porcine corneas. In the cornea, a quite homogenous stiffness map was found with a 190 kPa +/-32 kPa mean elasticity. The influence of photodynamic Riboflavin/UVA induced CXL was measured. A significant Young's modulus increase was obtained with a mean 890 kPa +/-250 kPsa posttreatment Young's modulus (460% increase), located in the anterior part of the cornea. Simulations based on 3-D time domain finite differences simulation were also performed and found to be in good agreement with ex vivo experiments. The SSI technique can perform real-time, noninvasive, high-resolution, and quantitative maps of the whole corneal elasticity. This technique could be real time and straightforward adapted for a very wide field of in vivo investigations. © 2006 IEEE. Mots-clés: Biomechanics; Cornea; Elastography; Stiffness; Ultrasound; Biomechanical response; Cornea; Cornea transplant; Corneal pathologies; Corneal refractive surgery; Elasticity measurement; Elastography; Ex-vivo; Femto-second laser; Fine tuning; High resolution; High-resolution measurements; In-vivo; Intra ocular pressure; Linear probe; Local elasticity; Noninvasive estimation; Porcine corneas; Post treatment; Quantitative evaluation; Quantitative imaging; Quantitative mapping; Real time; Remote palpat
Ultrasound-inducible fluorescent particles for internal tattooing Couture, O., N. Pannacci, A. Babataheri, P. Tabeling, M. Fink, M. Tanter, and V. Servois Proceedings - IEEE Ultrasonics Symposium (2009) Résumé: Our objective is to selectively and non-invasively deposits markers under image guidance for internal tattooing. This study describes the production of ultrasound-inducible particles carrying large payloads of fluorescent markers and the in vivo proof of concept of their remote deposit via focused ultrasound. The particles are double emulsions produced in a microfluidic system, consisting of aqueous fluorescein in perfluorocarbon in water. The vaporization threshold of these particles is measured with a 2.25 MHz transducer focused in an Opticell plate and observed under an inverted fluorescence microscope. The composite particles are monodisperse with a diameter of 5 microns. Fluorescein-containing water represents about 70% of the particles content and they are stable for weeks. When submitted to 2.25 MHz pulses, the particles vaporize at 4 MPa peak-negative pressure. During disruption, jets of fluorescein are generated. After several seconds, a brightly fluorescent dot (0.5 mm diameter) is observed at the focus of the transducer. Experiments in the chorioallantoique membrane of chicken eggs demonstrate that sufficient fluorescein can be released allows the observation by the naked eye. This localized internal tattooing could help surgeons identify tissue previously highlighted under image guidance. ©2009 IEEE. Mots-clés: Fluorescein; Registration; Sonoporation; Surgery; Ultrasound; Composite particles; Double emulsions; Fluorescein; Fluorescence microscopes; Fluorescent markers; Fluorescent particle; Focused ultrasound; Image guidances; In-vivo; Micro fluidic system; Monodisperse; Naked-eye; Negative pressures; Perfluorocarbons; Proof of concept; Sonoporation; Deposits; Fluorescence; Surgery; Transducers; Water content; Ultrasonics
Quantitative imaging of myocardium elasticity using supersonic shear imaging Couade, M., M. Pernot, M. Tanter, E. Messas, A. Bel, M. Ba, A.-A. Hagège, and M. Fink Proceedings - IEEE Ultrasonics Symposium (2009) Résumé: The concept of shear wave elastography is applied to the heart. The goal of this study is to demonstrate the potential of this technique for quantifying the elasticity time variation of the myocardium. Experiments are performed in vivo on N=10 sheep with a linear high frequency probe placed directly on the myocardium. The feasibility of generating and imaging the propagation of shear wave in the beating heart and estimating locally the myocardium elasticity at each stage of a single heart cycle is investigated by repeating acquisition of shear wave propagation between 10 and 20 times per second. The dependence of estimated shear modulus with probe angle (short axis to long axis), depth and left ventricle pressure is studied in vivo and ex vivo. The short term effect of a local ischemia is also studied by coronary arteries ligature, showing the sensitivity of the technique to a local loss of contractility in the myocardium. Finally, this study shows the potential of shear wave elastography as a quantification tool of myocardium mechanical properties. ©2009 IEEE. Mots-clés: Acoustic radiation force; Cardiac imaging; Contractility; Elastography; Myocardial stiffness; Shear wave; Ultrafast imaging; Acoustic radiation force; Cardiac imaging; Contractility; Elastography; Ultrafast imaging; Acoustic emissions; Acoustic radiators; Acoustic wave propagation; Acoustic wave transmission; Elasticity; Heart; Mechanical properties; Probes; Shear waves; Stiffness; Ultrasonic devices; Ultrasonics; Shear flow
3D in vivo brain elasticity mapping in small animals using ultrasound Macé, E., I. Cohen, J. L. Gennisson, G. Montaldo, R. Miles, M. Fink, and M. Tanter Proceedings - IEEE Ultrasonics Symposium (2009) Résumé: Supersonic Shear Imaging (SSI) is an ultrasound based technique for elasticity imaging that has been successfully tested on several organs in the framework of cancer diagnosis. In this work, the potential of this technique to map brain elasticity in vivo on trepanned small animals is investigated. From a SSI scan in the sagittal plane of the brain, a 3D elasticity map is reconstructed. A good correlation between the elasticity map and anatomy is observed. The values of dynamic modulus lie between 1 and 16 kPa and grey matter appears softer than white matter. The propagation of shear waves is found to be anisotropic in the cortex, which could be a consequence of the fiber orientation. Moreover, the good temporal resolution of this technique allows a dynamic estimation of brain elasticity within one single cardiac cycle. In the cortex, it is shown that the passage of the arterial pulse do not transiently modify elasticity. Next experiments will focus on applying this new technique in small animal models of neurological pathologies to estimate the effect of damaged tissues on elasticity. ©2009 IEEE. Mots-clés: Brain; Elastography; Small animal; Supersonic shear imaging; 3D elasticity; Arterial pulse; Cancer diagnosis; Cardiac cycles; Dynamic estimation; Dynamic moduli; Elasticity imaging; Elastography; Fiber orientations; Good correlations; Grey matters; In-vivo; Sagittal plane; Small Animal; Small animal model; Supersonic shear imaging; Temporal resolution; White matter; Animals; Three dimensional; Ultrasonic applications; Ultrasonics; Elasticity
MR-guided ultrasonic brain therapy: High frequency approach Aubry, J. F., L. Marsac, M. Pernot, M. Tanter, B. Robert, Y. Martin, C. Cohen-Bacrie, J. Souquet, and M. Fink Proceedings - IEEE Ultrasonics Symposium (2009) Résumé: A novel MR-guided brain therapy device operating at 1MHz has been designed and constructed. The system has been installed and tested in a clinical 1.5 T Philips Achieva MRI. Three dimensional time domain finite differences simulations were used to compute the propagation of the wave field through three human skulls. The simulated phase distortions were used as inputs for transcranial correction and the corresponding pressure fields were scanned in the focal plane. At half of the maximum power (10 W/cm2 on the surface of the transducers), necroses were induced 2 cm deep in turkey breasts placed behind a human skull. In vitro experiments on human skulls show that simulations restore more than 85% of the pressure level through the skull bone when compared to a control correction performed with an implanted hydrophone. Finally, high power experiments are performed though the skull bone and a MR-Thermometry sequence is used to map the temperature rise in a brain phantom every 3 s in two orthogonal planes (focal plane and along the axis of the probe). ©2009 IEEE. Mots-clés: HIFU; MR guided therapy; Transcranial therapy; Brain phantoms; Brain therapy; Focal Plane; High frequency; High-power; Human skull; In-vitro; Maximum power; MR-thermometry; Orthogonal plane; Phase distortions; Philips; Pressure field; Pressure level; Skull bone; Temperature rise; Three-dimensional time domain; Transcranial; Wavefields; Bone; Electroacoustic transducers; Focusing; Ultrasonics
Temperature dependence of the shear modulus of soft tissues assessed by ultrasound Sapin, E., J.-L. Gennisson, M. Pernot, M. Fink, and M. Tanter Proceedings - IEEE Ultrasonics Symposium (2009) Résumé: Ultrasound-based techniques to monitor HIFU treatments, combining temperature and elasticity mapping, require better understanding of the thermal effects on soft tissues elasticity. Hence, the study aims to evaluate the temperature dependence of the shear modulus of bovine muscles. Nine ex vivo samples of bovine muscle were slowly heated into a thermally-controlled saline bath. Thermocouples were used to assess temperatures into muscles. Local elasticity was assessed using Supersonic Shear Imaging. Samples were heated from 20 °C to 70 °C by steps of 10 °C and 20 min long and cooled back at room temperature. Elasticity assessment was achieved every minute along the muscular fibres. The shear modulus decreased linearly with increasing temperature up to 44 °C, with a change in slope around 37 °C. Then, it exponentially decreased from 44 °C to 56 °C. Finally, it exponentially increased for higher temperatures. The thermal-induced changes in the shear modulus of ex vivo bovine muscles using ultrasound are consistent with theorical changes of myosin and collagen microstructure. Given the high sensitivity of the ultrasound-based technique to the behaviour of both myofibrilar proteins and collagen on heating, this study gives promising prospects for the use of a full-ultrasound-based technique to monitor thermal effects on tissues. ©2009 IEEE. Mots-clés: Elasticity; Muscle; Supersonic shear imaging; Thermal effect; Bovine muscle; Ex-vivo; High sensitivity; Higher temperatures; Local elasticity; Room temperature; Shear modulus; Soft tissue; Supersonic shear imaging; Temperature dependence; Collagen; Elastic moduli; Elasticity; Histology; Shear strain; Temperature distribution; Thermocouples; Ultrasonic applications; Ultrasonics; Muscle
Ultrafast imaging of the heart using circular wave synthetic imaging with phased arrays Couade, M., M. Pernot, M. Tanter, E. Messas, A. Bel, M. Ba, A.-A. Hagège, and M. Fink Proceedings - IEEE Ultrasonics Symposium (2009) Résumé: The concept of synthetic imaging using circular wave is proposed to image with a very large field of view and at a very high frame rate (>1000 images/sec) heart motions with a conventional cardiac phased array probe. The goal of this study is to demonstrate in vivo the feasibility of this technique. Experiments are first performed in-vitro on ultrasound phantoms to optimize the trade-off between image quality and frame rate. An in vivo study is then performed on 10 sheep with a conventional phased array probe placed directly on the epicardium at different locations to obtain cine-loop of a complete heart cycle in the conventional imaging planes (long and short axis). After classical post processing of acquired cine-loop (wall tracking and tissue Doppler velocity estimation), the propagation of mechanical waves induced naturally during the heart cycle such as aortic and mitral valves closure can be observed. ©2009 IEEE. Mots-clés: Heart; Synthetic imaging; TDI; Ultrafast imaging; Circular waves; Conventional imaging; Frame rate; Heart motion; High frame rate; In-vitro; In-vivo; Mitral valves; Phased array probes; Phased arrays; Post processing; Synthetic imaging; Tissue Doppler; Ultrafast imaging; Ultrasound phantom; Very large field of view; Wall tracking; Image quality; Probes; Ultrasonic applications; Ultrasonics; Valves (mechanical); Heart
Effects of nonlinearity on propagation through the skull Pinton, G. F., J.-F. Aubry, M. Tanter, and M. Fink Proceedings - IEEE Ultrasonics Symposium (2009) Résumé: As an ultrasound wave propagates nonlinearly energy is transferred to higher frequencies where it is more strongly attenuated. Compared to soft tissue the skull has a strongly heterogeneous material parameters. We characterize with experiments and establish a numerical method that can describe the effects of the skull on the nonlinear components of ultrasonic wave propagation for application to high intensity focused ultrasound (HIFU) therapy in the brain. ©2009 IEEE. Mots-clés: Heterogeneous materials; High intensity focused ultrasound; Higher frequencies; Non-Linearity; Nonlinear components; Soft tissue; Ultrasound waves; Ultrasonic testing; Ultrasonic waves; Ultrasonics
MR guidance, monitoring and control of Brain HIFU therapy in small animals: In vivo demonstration in rats at 7T Larrat, B., M. Pernot, E. Dervishi, A. Souilah, D. Seilhean, Y. Marie, A. L. Boch, J. F. Aubry, M. Fink, and M. Tanter Proceedings - IEEE Ultrasonics Symposium (2009) Résumé: In the framework of HIFU transcranial brain therapy, it is mandatory to develop techniques capable of assessing the focusing quality and location before the treatment. Monitoring heat deposition in real time and verifying the extension of the treated area are also important steps. In this study, an imaging protocol is proposed to:1/ locate the US radiation force induced displacement in tissues and quantify the acoustic pressure at focus prior to HIFU; 2/ monitor the temperature rise during HIFU; and 3/ assess the changes in elasticity in the treated area. A 7T MRI scanner was equipped with a home-made stereotactic frame for rats and a US focused transducer working at 1.5MHz. Such a tool is key for the evaluation of the biological effects of HIFU on brain tissue and tumors. The proposed protocol was successfully tested on 12 rats with and without injected tumors. The accurate localization of the focal point prior to HIFU was demonstrated in vivo. Furthermore, the pressure estimation in situ allowed to accurately simulate the heat deposition at focus and to plan the treatment (electrical power, duration). The temperature measurements were in good accordance with the predicted curves. The elasticity maps showed significant changes after treatment in some cases. ©2009 IEEE. Mots-clés: Brain; Focused ultrasound; High intensity; Magnetic resonance elastography; Magnetic resonance thermometry; Monitoring; Radiation force localization; Rat; Transcranial; Focused ultrasound; High intensity; Magnetic resonance elastography; Radiation force localization; Radiation forces; Transcranial; Animals; Elasticity; Magnetic resonance; Rats; Scanning; Temperature measurement; Temperature sensors; Thermometers; Tumors; Ultrasonics; Monitoring
Mapping myocardial elasticity changes after RF-ablation using supersonic shear imaging Pernot, M., E. Macé, R. Dubois, M. Couade, M. Fink, and M. Tanter Computers in Cardiology 36, 793-796 (2009) Résumé: Shear Wave Imaging was used to monitor radiofrequency ablation (RFA) of myocardial tissues in vivo and in vitro. This technique was used to quantify and to map the myocardial stiffness before and after cardiac ablation. Experiments were performed in vivo on a sheep and in vitro samples of bovine muscle. The feasibility of mapping the myocardial elasticity was demonstrated in vitro after RFA. A strong increase of the myocardial stiffness was found after RFA. In vivo, the normal variation of the myocardial stiffness was measured during the cardiac cycle. The Young's modulus was found 8 times higher in the systolic phase than in the diastolic phase. During ablation a significant increase of the Young's modulus was observed in the diastolic phase whereas a sudden decrease was observed in systole. Mots-clés: Before and after; Bovine muscle; Cardiac ablation; Cardiac cycles; In-vitro; In-vivo; Myocardial tissue; Radiofrequency ablation; Shear wave imaging; Supersonic shear imaging; Young's Modulus; Cardiology; Elastic moduli; Elasticity; Stiffness; Ultrasonic devices; Ablation
Invariants of the time-reversal operator for a dielectric cylinder using different Tx and Rx arrays Davy, M., J.-G. Minonzio, C. Prada, J. D. Rosny, and M. Fink IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) (2009)
Focusing and amplification of electromagnetic waves by time-reversal in an leaky reverberation chamber Davy, M., J. De Rosny, and M. Fink IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) (2009)
Non-invasive transcranial ultrasound therapy based on a 3D CT scan: Protocol validation and in vitro results Marquet, F., M. Pernot, J.-F. Aubry, G. Montaldo, L. Marsac, M. Tanter, and M. Fink Physics in Medicine and Biology 54, no. 9, 2597-2613 (2009) Résumé: A non-invasive protocol for transcranial brain tissue ablation with ultrasound is studied and validated in vitro. The skull induces strong aberrations both in phase and in amplitude, resulting in a severe degradation of the beam shape. Adaptive corrections of the distortions induced by the skull bone are performed using a previous 3D computational tomography scan acquisition (CT) of the skull bone structure. These CT scan data are used as entry parameters in a FDTD (finite differences time domain) simulation of the full wave propagation equation. A numerical computation is used to deduce the impulse response relating the targeted location and the ultrasound therapeutic array, thus providing a virtual time-reversal mirror. This impulse response is then time-reversed and transmitted experimentally by a therapeutic array positioned exactly in the same referential frame as the one used during CT scan acquisitions. In vitro experiments are conducted on monkey and human skull specimens using an array of 300 transmit elements working at a central frequency of 1 MHz. These experiments show a precise refocusing of the ultrasonic beam at the targeted location with a positioning error lower than 0.7 mm. The complete validation of this transcranial adaptive focusing procedure paves the way to in vivo animal and human transcranial HIFU investigations. © 2009 Institute of Physics and Engineering in Medicine. Mots-clés: Adaptive corrections; Adaptive focusing; Beam shapes; Brain tissue; Central frequency; CT scan; Finite difference; Full waves; Human skull; In-phase; In-vitro; In-vivo; Non-invasive; Numerical computations; Positioning error; Protocol validation; Skull bone; Time domain; Time-reversed; Transcranial; Transcranial ultrasound; Ultrasonic beams; Virtual-time; Acoustic fields; Acoustic waves; Bone; Experiments; Finite difference time domain method; Geometrical optics; Impulse response; Mammals; Tomog
Design and characterization of bubble phononic crystals Leroy, V., A. Bretagne, M. Fink, H. Willaime, P. Tabeling, and A. Tourin Applied Physics Letters 95, no. 17 (2009) Résumé: We report the practical realization of phononic crystals with gas inclusions, using soft lithography techniques. Ultrasonic experiments from 0.3 to 5 MHz confirm the existence of deep and wide minima of transmission through the crystal. We show that the first gap is due to the combined effects of Bragg reflections and bubble resonances. We propose a simple layered model that gives a reasonable prediction of the ultrasonic transmission. © 2009 American Institute of Physics. Mots-clés: Bragg reflection; Combined effect; Gas inclusions; Layered model; Phononic Crystal; Practical realizations; Soft lithography; Ultrasonic experiments; Phonons; Ultrasonics; Crystals
Application of DENSE-MR-elastography to the human heart Robert, B., R. Sinkus, J.-L. Gennisson, and M. Fink Magnetic Resonance in Medicine 62, no. 5, 1155-1163 (2009) Résumé: Typically, MR-elastography (MRE) encodes the propagation of monochromatic acoustic waves in the MR-phase images via sinusoidal gradients characterized by a detection frequency equal to the frequency of the mechanical vibration. Therefore, the echo time of a conventional MRE sequence is typically longer than the vibration period which is critical for heart tissue exhibiting a short T 2. Thus, fast acquisition techniques like the so-called fractional encoding of harmonic motions were developed for cardiac applications. However, fractional encoding of harmonic motions is limited since it is two orders of magnitude less sensitive to motion than conventional MRE sequences for low-frequency vibrations. Here, a new sequence is derived from the so-called displacement encoding with stimulated echoes (DENSE) sequence. This sequence is more sensitive to displacement than fractional encoding of harmonic motions, and its spectral specificity is equivalent to conventional MRE sequences. The theoretical spectral properties of this new motion-encoding technique are validated in a phantom and excised pork heart specimen. An excellent agreement is found for the measured displacement fields using classic MRE and displacement encoding with stimulated echoes MRE (8% maximum difference). In addition, initial in vivo results on a healthy volunteer clearly show propagating shear waves at 50 Hz. Thus, displacement encoding with stimulated echoes MRE is a promising technique for motion encoding within short T 2* materials. © 2009 Wiley-Liss, Inc. Mots-clés: Fast MR-elastography; In vivo heart; Low frequency mechanical vibrations; Motion encoding; Short T 2* tissues; animal tissue; article; elastography; heart movement; human; human experiment; image processing; magnetic resonance elastography; mathematical model; nonhuman; normal human; nuclear magnetic resonance imaging; phantom; shear flow; vibration; Algorithms; Elastic Modulus; Elasticity Imaging Techniques; Heart; Humans; Image Enhancement; Image Interpretation, Computer-Assisted; Phantoms, Im
Ultrafast Imaging of Ultrasound Contrast Agents Couture, O., S. Bannouf, G. Montaldo, J.-F. Aubry, M. Fink, and M. Tanter Ultrasound in Medicine and Biology 35, no. 11, 1908-1916 (2009) Résumé: The disappearance of ultrasound contrast agents after disruption can provide useful information on their environment. However, in vivo acoustical imaging of this transient phenomenon, which has a duration on the order of milliseconds, requires high frame rates that are unattainable by conventional ultrasound scanners. In this article, ultrafast imaging is applied to microbubble tracking using a 128-element linear array and an elastography scanner. Contrast agents flowing in a wall-less tissue phantom are insonified with a high-intensity disruption pulse followed by a series of plane waves emitted at a 5 kHz PRF. A collection of compounded images depicting the evolution of microbubbles is obtained after the echoes are beamformed in silico. The backscattering of the microbubbles appears to increase in the first image after disruption (4 ms) and decrease following an exponential decay in the next hundred milliseconds. This microbubble dynamic depends on the length and amplitude of the high-intensity pulse. Furthermore, confined microbubbles are found to differ significantly from their free-flowing counterparts in their dissolution curves. The high temporal resolution provided by ultrafast imaging could help distinguish targeted microbubbles during molecular imaging. (E-mail: ). © 2009 World Federation for Ultrasound in Medicine & Biology. Mots-clés: Disruption; Dissolution; Microbubbles; Molecular imaging; Plane waves; Targeted contrast agents; Ultrafast; Microbubbles; Molecular imaging; Plane waves; Targeted contrast agents; Ultra-fast; Acoustic waves; Scanning; Ultrasonics; Dissolution; echo contrast medium; amplitude modulation; article; B scan; computer model; contrast enhancement; controlled study; elastography; image analysis; image processing; imaging system; microbubble; molecular imaging; phantom; priority journal; radiation scatte
Energy-based adaptive focusing of waves: application to noninvasive aberration correction of ultrasonic wavefields Herbert, E., M. Pernot, G. Montaldo, M. Fink, and M. Tanter IEEE transactions on ultrasonics, ferroelectrics, and frequency control 56, no. 11, 2388-2399 (2009) Résumé: An aberration correction method based on the maximization of the wave intensity at the focus of an emitting array is presented. The potential of this new adaptive focusing technique is investigated for ultrasonic focusing in biological tissues. The acoustic intensity is maximized noninvasively through direct measurement or indirect estimation of the beam energy at the focus for a series of spatially coded emissions. For ultrasonic waves, the acoustic energy at the desired focus can be indirectly estimated from the local displacements induced in tissues by the ultrasonic radiation force of the beam. Based on the measurement of these displacements, this method allows determination of the precise estimation of the phase and amplitude aberrations, and consequently the correction of aberrations along the beam travel path. The proof of concept is first performed experimentally using a large therapeutic array with strong electronic phase aberrations (up to 2pi). Displacements induced by the ultrasonic radiation force at the desired focus are indirectly estimated using the time shift of backscattered echoes recorded on the array. The phase estimation is deduced accurately using a direct inversion algorithm which reduces the standard deviation of the phase distribution from sigma = 1.89 radian before correction to sigma = 0.53 radian following correction. The corrected beam focusing quality is verified using a needle hydrophone. The peak intensity obtained through the aberrator is found to be -7.69 dB below the reference intensity obtained without any aberration. Using the phase correction, a sharp focus is restored through the aberrator with a relative peak intensity of -0.89 dB. The technique is tested experimentally using a linear transmit/receive array through a real aberrating layer. The array is used to automatically correct its beam quality, as it both generates the radiation force with coded excitations and indirectly estimates the acoustic intensity at the focus with speckle tracking. This technique could have important implications in the field of high-intensity focused ultrasound even in complex configurations such as transcranial, transcostal, or deep seated organs. Mots-clés: article; artifact; computer aided design; echography; equipment; equipment design; evaluation; image enhancement; instrumentation; methodology; reproducibility; sensitivity and specificity; Artifacts; Computer-Aided Design; Equipment Design; Equipment Failure Analysis; Image Enhancement; Reproducibility of Results; Sensitivity and Specificity; Ultrasonography
Manipulating Spatiotemporal Degrees of Freedom of Waves in Random Media Lemoult, F., G. Lerosey, J. De Rosny, and M. Fink Physical Review Letters 103, no. 17 (2009) Résumé: We show that all the spatiotemporal degrees of freedom available in a complex medium can be harnessed and converted into spatial ones. This is demonstrated experimentally through an instantaneous spatial inversion, using broadband ultrasonic waves in a multiple scattering sample. We show theoretically that the inversion convergence is governed by the total number of degrees of freedom available in the medium for a fixed bandwidth and demonstrate experimentally its use for complex media investigation. We believe our approach has potential in sensing, imagery, focusing, and telecommunication. © 2009 The American Physical Society. Mots-clés: Complex media; Complex medium; Degrees of freedom; Number of degrees of freedom; Waves in random media; Ultrasonics; Mechanics
Theory of the time-reversal operator for a dielectric cylinder using separate transmit and receive arrays Minonzio, J.-G., M. Davy, J. De Rosny, C. Prada, and M. Fink IEEE Transactions on Antennas and Propagation 57, no. 8, 2331-2340 (2009) Résumé: The DORT method applies to scattering analysis with arrays of transceivers. It consists in the study of the time-reversal invariants. In this paper, a large dielectric cylinder is observed by separate transmit and receive arrays with linear polarizations, E or H, parallel to its axis. The decomposition of the scattered field into normal modes and projected harmonics is used to determine the theoretical time-reversal invariants. It is shown that the number of invariants is about 2k1a, where a is the cylinder radius and k1 the wave number in the surrounding medium. Furthermore, this approach provides approximated expressions of the two first invariants for a sub-resolved cylinder, i.e., when the cylinder diameter is smaller than the resolution width of the arrays. The two first invariants are also expressed in the small object limit for k1 a < 0.5. AMS subject classifications. 35B40, 35P25, 45A05, 74J20,78M35 © 2009 IEEE. Mots-clés: Antenna array processing; Electromagnetic inverse problem; Electromagnetic scattering; Cylinder diameters; Dielectric cylinder; Electromagnetic inverse problem; Electromagnetic scattering; Linear polarization; Normal modes; Scattered field; Scattering analysis; Small objects; Subject classification; Time-reversal; Time-reversal operator; Wave numbers; Antenna arrays; Array processing; Dielectric devices; Dielectric materials; Electromagnetic wave scattering; Electromagnetism; Inverse problems; M
Ultrasonic focusing through the ribs using the DORT method Cochard, E., C. Prada, J. F. Aubry, and M. Fink Medical Physics 36, no. 8, 3495-3503 (2009) Résumé: Thermal ablation induced by high intensity focused ultrasound has produced promising clinical results to treat hepatocarcinoma and other liver tumors. However skin burns have been reported due to the high absorption of ultrasonic energy by the ribs. This study proposes a method to produce an acoustic field focusing on a chosen target while sparing the ribs using the decomposition of the time-reversal operator (DORT method). The idea is to apply an excitation weight vector to the transducers array which is orthogonal to the subspace of emissions focusing on the ribs. A linear array of transducers has been used to measure the set of singular vectors associated with a chest phantom, made of three human ribs immersed in water, and to produce the desired acoustic fields. The resulting propagating fields have been measured both in the focal plane and in the plane of the ribs using a needle hydrophone. The ratio of the energies absorbed at the focal point and on the ribs has been enhanced up to 100-fold, as demonstrated by the measured specific absorption rates. © 2009 American Association of Physicists in Medicine. Mots-clés: Adaptive focusing; DORT; High intensity focused ultrasound; Noninvasive surgery; Phased array; acoustics; article; energy absorption; phantom; priority journal; radiation energy; rib; ultrasound; ultrasound transducer; Absorption; Humans; Male; Phantoms, Imaging; Ribs; Thorax; Time Factors; Ultrasonic Therapy
Energy-based adaptive focusing of waves: Application to ultrasonic transcranial therapy Herbert, E., M. Pernot, G. Montaldo, M. Tanter, and M. Fink AIP Conference Proceedings 1113, 8-12 (2009) Résumé: We propose a general concept of adaptive focusing through complex media based on the estimation or measurement of the wave energy density at the desired focal spot. As it does not require the knowledge of phase information, this technique has many potential applications in acoustics and optics for light focusing through diffusive media. We present here the application of this technique to the problem of ultrasonic aberration correction for HIFU treatments. The estimation of wave energy density is based on the maximization of the ultrasound radiation force, using a multi-elements (64) array. A spatial coded excitation method is developed by using ad-hoc virtual transducers that include all the elements for each emission. The radiation force is maximized by optimizing the displacement of a small target at the focus. We measured the target displacement using ultrasound pulse echo on the same elements. A method using spatial coded excitation is developed in order to estimate the phase and amplitude aberration based on the target displacement. We validated this method using phase aberration up to 2π. The phase correction is achieved and the pressure field is measured using a needle hydrophone. The acoustic intensity at the focus is restored through very large aberrations. Basic experiments for brain HIFU treatment are presented. Optimal transcranial adaptive focusing is performed using a limited number of short ultrasonic radiation force pushes. © 2009 American Institute of Physics. Mots-clés: Aberrations; Adaptive focusing; Focused ultrasound; HIFU; Transcranial therapy
Cavitation bubble generation and control for HIFU transcranial adaptive focusing Gâteau, J., L. Marsac, M. Pernot, J.-F. Aubry, M. Tanter, and M. Fink AIP Conference Proceedings 1113, 18-22 (2009) Résumé: Brain treatment with High Intensity Focused Ultrasound (HIFU) can be achieved by multichannel arrays through the skull using time-reversal focusing. Such a method requires a reference signal either sent by a real source embedded in brain tissues or computed from a virtual source, using the acoustic properties of the skull deduced from CT images. This noninvasive computational method allows precise focusing, but is time consuming and suffers from unavoidable modeling errors which reduce the accessible acoustic pressure at the focus in comparison with real experimental time-reversal using an implanted hydrophone. Ex vivo simulations with a half skull immersed in a water tank allow us to reach at low amplitude levels a pressure ratio of 83% of the reference pressure (real time reversal) at 1MHz. Using this method to transcranially focus a pulse signal in an agar gel (model for in vivo bubble formation), we induced a cavitation bubble that generated an ultrasonic wave received by the array. Selecting the 1MHz component, the signal was time reversed and re-emitted, allowing 97%±1.1% of pressure ratio to be restored. To target points in the vicinity of the geometrical focus, electronic steering from the reference signal has been achieved. Skull aberrations severely degrade the accessible pressure while moving away from the focus ( ̃90% at 10mm in the focal plane). Nevertheless, inducing cavitation bubbles close to the limit of the primary accessible zone allowed us to acquire multiple references signal to increase the electronic steering area by 50%. © 2009 American Institute of Physics. Mots-clés: Cavitation bubble; Non invasive method; Transcranial brain therapy; Ultrasonic adaptive focusing; Ultrasonic array
Time-reversed waves and super-resolution Fink, M., J. De Rosny, G. Lerosey, and A. Tourin Comptes Rendus Physique 10, no. 5, 447-463 (2009) Résumé: Time-reversal mirrors (TRMs) refocus an incident wavefield to the position of the original source regardless of the complexity of the propagation medium. TRMs have now been implemented in a variety of physical scenarios from GHz microwaves to MHz ultrasonics and to hundreds of Hz in ocean acoustics. Common to this broad range of scales is a remarkable robustness exemplified by observations at all scales that the more complex the medium (random or chaotic), the sharper the focus. A TRM acts as an antenna that uses complex environments to appear wider than it is, resulting for a broadband pulse, in a refocusing quality that does not depend on the TRM aperture. Moreover, when the complex environment is located in the near field of the source, time-reversal focusing opens completely new approaches to super-resolution. We will show that, for a broadband source located inside a random metamaterial, a TRM located in the far field radiated a time-reversed wave that interacts with the random medium to regenerate not only the propagating but also the evanescent waves required to refocus below the diffraction limit. This focusing process is very different from that developed with superlenses made of negative index material only valid for narrowband signals. We will emphasize the role of the frequency diversity in time-reversal focusing. To cite this article: M. Fink et al., C. R. Physique 10 (2009). © 2009. Mots-clés: Metamaterials; Time-reversal mirror
Time-reversal focusing of therapeutic ultrasound on targeted microbubbles Couture, O., J.-F. Aubry, M. Tanter, and M. Fink Applied Physics Letters 94, no. 17 (2009) Résumé: Targeted microbubbles bind specifically to molecular markers of diseases and their unique acoustic signature is used to image cellular processes in vivo. The ability of time-reversal processing to focus waves through heterogeneities on such targeted microbubbles is demonstrated. For this purpose, microbubbles were deposited on a gelatin phantom and their specific signal was recorded by a high intensity ultrasonic array. The amplified time-reversed signal was re-emitted and shown to focus back in the region where the bound microbubbles were present. This proof of concept emphasizes that molecular-time-reversal focusing could guide energy deposition on early, diffuse, or metastatic disease. © 2009 American Institute of Physics. Mots-clés: Acoustic signatures; Cellular process; Energy depositions; Gelatin phantoms; High-intensity ultrasonic; In-vivo; Metastatic disease; Micro-bubbles; Molecular markers; Proof of concepts; Targeted microbubbles; Therapeutic ultrasounds; Time-reversal focusing; Time-reversal processing; Time-reversed; Ultrasonics; Ultrasonic imaging
Coherent plane-wave compounding for very high frame rate ultrasonography and transient elastography Montaldo, G., M. Tanter, J. Bercoff, N. Benech, and M. Fink IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 56, no. 3, 489-506 (2009) Résumé: The emergence of ultrafast frame rates in ultrasonic imaging has been recently made possible by the development of new imaging modalities such as transient elastography. Data acquisition rates reaching more than thousands of images per second enable the real-time visualization of shear mechanical waves propagating in biological tissues, which convey information about local viscoelastic properties of tissues. The first proposed approach for reaching such ultrafast frame rates consists of transmitting plane waves into the medium. However, because the beamforming process is then restricted to the receive mode, the echographic images obtained in the ultrafast mode suffer from a low quality in terms of resolution and contrast and affect the robustness of the transient elastography mode. It is here proposed to improve the beamforming process by using a coherent recombination of compounded plane-wave transmissions to recover high-quality echographic images without degrading the high frame rate capabilities. A theoretical model is derived for the comparison between the proposed method and the conventional B-mode imaging in terms of contrast, signal-to-noise ratio, and resolution. Our model predicts that a significantly smaller number of insonifications, 10 times lower, is sufficient to reach an image quality comparable to conventional B-mode. Theoretical predictions are confirmed by in vitro experiments performed in tissue-mimicking phantoms. Such results raise the appeal of coherent compounds for use with standard imaging modes such as B-mode or color flow. Moreover, in the context of transient elastography, ultrafast frame rates can be preserved while increasing the image quality compared with flat insonifications. Improvements on the transient elastography mode are presented and discussed. © 2006 IEEE. Mots-clés: Acquisition rates; B-mode imaging; Biological tissues; Color flows; Echographic images; Frame rates; High frame rates; High qualities; Imaging modalities; Imaging modes; In-vitro; Low qualities; Plane waves; Plane-wave transmissions; Real-time visualizations; Receive modes; Signal-to-noise ratios; Theoretical models; Theoretical predictions; Tissue-mimicking phantoms; Transient elastography; Ultra fasts; Visco-elastic properties; Beamforming; Data visualization; Echocardiography; Histology; Laws
The time-reversal operator with virtual transducers: Application to far-field aberration correction Robert, J.-L., and M. Fink Journal of the Acoustical Society of America 124, no. 6, 3659-3668 (2009) Résumé: The decomposition of the time-reversal operator (DORT) is a detection and focusing technique using an array of transmit receive transducers. It can extract Green's functions of scatterers in a medium. A variant consists in transmitting focused beams (FDORT). It is shown here that the FDORT method can be interpreted as the decomposition of a time-reversal operator between an array of virtual transducers located at the transmit beams' foci and the physical array. The receive singular vectors correspond to scatterers' Green's functions expressed in the physical array while the transmit singular vectors correspond to Green's functions expressed in the virtual array. The position of the virtual array can be changed by varying the position of the foci, thus offering different points of view. Parameters and performance of some transmit schemes are discussed. Appropriately positioning the virtual transducers can simplify some problems. One application is measuring and correcting aberration in the case of a far-field phase screen model. Placing the virtual transducers near the phase screen transforms the problem in a simpler near-field phase screen problem. © 2008 Acoustical Society of America. Mots-clés: Aberration corrections; Far fields; Focused beams; Focusing techniques; Near fields; Phase screens; Singular vectors; Time-reversal operators; Virtual arrays; Aberrations; Differential equations; Fourier transforms; Functions; Probability density function; Projection screens; Transducers; Green's function; Acoustics; Computer Simulation; Fourier Analysis; Models, Theoretical; Time Factors; Transducers; User-Computer Interface
Photoacoustic guidance of high intensity focused ultrasound with selective optical contrasts and time-reversal Funke, A. R., J.-F. Aubry, M. Fink, A.-C. Boccara, and E. Bossy Applied Physics Letters 94, no. 5, 054102 (2009) Résumé: The authors present a method of focusing high intensity ultrasound by time-reversing the photoacoustic response of an optically selective target in a nonselective background. The target's photoacoustic response was isolated from the background by subtracting the photoacoustic waveforms obtained at different optical wavelengths and convolved with a continuous signal. It was found that the focus produced was comparable in quality to that obtained by delay-law beam-forming. The method holds the promise of allowing precise targeting of high intensity focused ultrasound on nonechogenic targets, in moving environments, independently of the presence of aberrating layers. © 2009 American Institute of Physics. Mots-clés: Acoustic waves; Sonochemistry; Targets; Ultrasonic testing; Ultrasonics; Beam-forming; High intensity ultrasounds; High-intensity focused ultrasounds; Optical contrasts; Optical wavelengths; Time reversals; Wave forms; Photoacoustic effect
Quantitative Viscoelasticity Mapping of Human Liver Using Supersonic Shear Imaging: Preliminary In Vivo Feasability Study Muller, M., J.-L. Gennisson, T. Deffieux, M. Tanter, and M. Fink Ultrasound in Medicine and Biology 35, no. 2, 219-229 (2009) Résumé: This paper demonstrates the feasibility of in vivo quantitative mapping of liver viscoelasticity using the concept of supersonic shear wave imaging. This technique is based on the combination of a radiation force induced in tissues by focused ultrasonic beams and a very high frame rate ultrasound imaging sequence capable of catching in real time the transient propagation of resulting shear waves. The local shear wave velocity is recovered using a dedicated time-of-flight estimation technique and enables the 2-D quantitative mapping of shear elasticity. This imaging modality is performed using a conventional ultrasound probe during a standard intercostal ultrasonographic examination. Three supersonic shear imaging (SSI) sequences are applied successively in the left, middle and right parts of the 2-D ultrasonographic image. Resulting shear elasticity images in the three regions are concatenated to provide the final image covering the entire region-of-interest. The ability of the SSI technique to provide a quantitative and local estimation of liver shear modulus with a millimetric resolution is proven in vivo on 15 healthy volunteers. Liver moduli extracted from in vivo data from healthy volunteers are consistent with those reported in the literature (Young's modulus ranging from 4 to 7.5 kPa). Moreover, liver stiffness estimation using the SSI mode is shown to be fast (less than one second), repeatable (5.7% standard deviation) and reproducible (6.7% standard deviation). This technique, used as a complementary tool for B-mode ultrasound, could complement morphologic information both for fibrosis staging and hepatic lesions imaging (E-mail: ). © 2009 World Federation for Ultrasound in Medicine & Biology. Mots-clés: Liver fibrosis; Shear wave imaging; Transient elastography; Ultrasound; Estimation techniques; Frame rates; Hepatic lesions; In-vivo; Liver fibrosis; Local estimation; Radiation force (RF); Shear elasticity; Shear modulus; Shear wave imaging; Shear wave velocity (SWV); Time-of-flight (TOF); Transient elastography; Transient propagation; Ultrasound; Ultrasound (US) images; Young's modulus (IGC: E14/K14); Acoustic waves; Animal cell culture; Elastic moduli; Elastic waves; Elasticity; Estimation; L
The prolate spheroidal wave functions as invariants of the time reversal operator for an extended scatterer in the Fraunhofer approximation Robert, J.-L., and M. Fink Journal of the Acoustical Society of America 125, no. 1, 218-226 (2009) Résumé: The decomposition of the time reversal operator, known by the French acronym DORT, is widely used to detect, locate, and focus on scatterers in various domains such as underwater acoustics, medical ultrasound, and nondestructive evaluation. In the case of point-scatterers, the theory is well understood: The number of nonzero eigenvalues is equal to the number of scatterers, and the eigenvectors correspond to the scatterers Green's function. In the case of extended objects, however, the formalism is not as simple. It is shown here that, in the Fraunhofer approximation, analytical solutions can be found and that the solutions are functions called prolate spheroidal wave-functions. These functions have been studied in information theory as a basis of band-limited and time-limited signals. They also arise in optics. The theoretical solutions are compared to simulation results. Most importantly, the intuition that for an extended objects, the number of nonzero eigenvalues is proportional to the number of resolution cell in the object is justified. The case of three-dimensional objects imaged by a two-dimensional array is also dealt with. Comparison with previous solutions is made, and an application to super-resolution of scatterers is presented. © 2009 Acoustical Society of America. Mots-clés: Eigenvalues (of graphs); Eigenvectors; Fraunhofer approximations; Non destructive evaluation (NDE); Resolution cell; Simulation results; Super resolution (SR); Time reversal operator (DORT method); Differential equations; Functions; Green's function; Information theory; Programming theory; Quantum theory; Three dimensional; Ultrasonic applications; Underwater acoustics; Underwater audition; Wave functions; Probability density function
Time-reversal waves and super resolution Fink, M. Journal of Physics: Conference Series 124 (2008) Résumé: Time-reversal mirrors (TRMs) refocus an incident acoustic field to the position of the original source regardless of the complexity of the propagation medium. TRM's have now been implemented in a variety of physical scenarios from MHz ultrasonics with order centimeter aperture size to hundreds/thousands of Hz in ocean acoustics with order hundred meter aperture size. Common to this broad range of scales is a remarkable robustness exemplified by observations at all scales that the more complex the medium between the probe source and the TRM, the sharper the focus. The relation between the medium complexity and the size of the focal spot is studied in this paper. It is certainly the most exciting property of TRM compared to standard focusing devices. A TRM acts as an antenna that uses complex environments to appears wider than it is, resulting for a broadband pulse in a refocusing quality that does not depend of the TRM aperture. In this paper, we investigate the time-reversal approach in various media of increasing complexity We will also demonstrated that time-reversal focusing opens completely new approaches to super-resolution. We will show that in medium made of random distribution of sub-wavelength scatterers, a time-reversed wave field interacts with the random medium to regenerate not only the propagating but also the evanescent waves required to refocus below the diffraction limit. Finally, we will discuss the link existing between time-reversal approaches and new imaging methods recently developed where Green's functions of complex media can be extracted from diffusive noise by cross-correlating the recordings of a diffuse random wave field. © 2008 IOP Publishing Ltd. Mots-clés: Aperture sizes; Broadband pulse; Complex environments; Complex media; Diffraction limits; Evanescent wave; Focal spot; Focusing device; Imaging method; Medium complexity; Ocean acoustics; Physical scenario; Probe source; Random distribution; Random medium; Random waves; Sub-wavelength; Super resolution; Time-reversal; Time-reversal focusing; Time-reversed; Wavefields; Acoustic fields; Diffraction; Inverse problems; Differential equations
Radiation force localization of HIFU therapeutic beams coupled with Magnetic Resonance-Elastography treatment monitoring, In vivo application to the rat brain Larrat, B., M. Pernot, J.-F. Aubry, R. Sinkus, M. Tanter, and M. Fink Proceedings - IEEE Ultrasonics Symposium, 451-454 (2008) Résumé: Magnetic resonance elastography is feasible in the brain and is a new way to non invasively control the stiffness of the tissue. The thermal HIFU necrosis of the brain results in an increase of its complex shear modulus. Furthermore, MR sequences can be very sensitive to motion and thus give a good tool to detect the acoustic radiation force in in-vivo. This target control can be very valuable in order to assess the quality of the aberration correction when a high power US signal is about to be sent trough the skull. In this context, ex-vivo and in-vivo experiments were conducted with and without an aberrating skull. They confirmed that both the MR localization of the US focal point and the measurement of the tissue stiffness pre and post HIFU, together with temperature control during HIFU are valuable and feasible techniques for the accurate monitoring of HIFU in the brain. ©2008 IEEE. Mots-clés: Aberration correction; Acoustic radiation force; Complex shear modulus; Elastography; Ex-vivo; Focal points; High-power; In-vivo; In-vivo experiments; Magnetic resonance elastography; MR sequence; Radiation forces; Rat brain; Therapeutic beams; Tissue stiffness; Treatment monitoring; Magnetic resonance; Stiffness; Monitoring
Non-invasive quantitative imaging of arterial wall elasticity using supersonic shear imaging Couade, M., M. Pernot, M. Tanter, C. Prada, E. Messas, and M. Fink Proceedings - IEEE Ultrasonics Symposium, 946-949 (2008) Résumé: The concept of shear wave elasticity imaging is applied arteries. The goal of this study is to demonstrate the potential this technique for precisely and non-invasively quantifying the of the arterial wall. Experiments are performed in phantoms composed of elastic cylindrical shells that have elastic modulus in the range of human arteries stiffness. The of imaging the shear wave propagation in real-time measuring the frequency dispersion over a large bandwidth (100-1500 Hz) is demonstrated with good accuracy. Experimental curves are in good agreement with the theoretical computed for each phantom. Based on the dispersion, a simple method is developed to derive the elastic of the arterial wall. Finally, the feasibility of quantifying invasively the elastic modulus of the arterial wall is in vivo on healthy volunteers. ©2008 IEEE. Mots-clés: Acoustic radiation force; Arterial stiffness; Elastography; Shear wave; Ultrafast imaging; Acoustic radiation force; Arterial stiffness; Arterial wall; Elastic cylindrical shell; Elasticity imaging; Elastography; Experimental curves; Frequency dispersion; Human artery; In-vivo; Non-invasive; Quantitative imaging; SIMPLE method; Supersonic shear imaging; Ultrafast imaging; Acoustic emissions; Acoustic radiators; Acoustic wave propagation; Acoustic wave transmission; Acoustics; Elastic moduli; Ela
ShearWaveTM elastography: A new real time imaging mode for assessing quantitatively soft tissue viscoelasticity Bercoff, J., A. Criton, C. C. Bacrie, J. Souquet, M. Tanter, J. L. Gennisson, T. Deffieux, M. Fink, V. Juhan, A. Colavolpe, D. Amy, and A. Athanasiou Proceedings - IEEE Ultrasonics Symposium, 321-324 (2008) Résumé: ShearWaveTM Elastography (SWE) is a new real time ultrasound imaging mode that quantitatively measures local tissue elasticity in kPa. Based on the Supersonic Shear Imaging concept (developped at the Laboratoire Ondes et Acoustique, Paris), this new concept may appear as a promising tool to improve breast lesion characterization. In vitro experimental measurements have been performed to quantify SWE mode performances in terms of resolution, penetration and the ability to measure quantitatively elasticity. Results show that the SWE mode exhibits a millimetric resolution and quantifies properly tissue elasticity on a wide range of elastic contrasts (from 7 to 110 kPa). The real time capabilities and the robustness of the mode have been tested in clinical conditions, on breast lesions. 150 patients have been scanned with SWE mode in three different sites. Results show that SWE performs well on breast pathologies and presents a very good inter-site reproducibility. Finally, the quantitative elasticity value was analyzed as a function of pathology using FNA or core biopsy as the reference diagnostic method. © 2008 IEEE. Mots-clés: Elasticity; Elastography; kPa; Mach cone; Quantitative; Shear wave; Supersonic; Transient; Viscosity; Elastography; kPa; Mach cone; Quantitative; Supersonic; Elasticity; Pathology; Shear waves; Ultrasonics; Viscosity; Ultrasonic imaging
Electrical impedance tomography by elastic deformation Ammari, H., E. Bonnetier, Y. Capdeboscq, M. Tanter, and M. Fink SIAM Journal on Applied Mathematics 68, no. 6, 1557-1573 (2008) Résumé: This paper presents a new algorithm for conductivity imaging. Our idea is to extract more information about the conductivity distribution from data that have been enriched by coupling impedance electrical measurements to localized elastic perturbations. Using asymptotics of the fields in the presence of small volume inclusions, we relate the pointwise values of the energy density to the measured data through a nonlinear PDE. Our algorithm is based on this PDE and takes full advantage of the enriched data. We give numerical examples that illustrate the performance and the accuracy of our approach. © 2008 Society for Industrial and Applied Mathematics. Mots-clés: 0-Laplacian; Asymptotic formula; Elastic perturbation; Electrical impedance tomography; Reconstruction; Substitution algorithm; 0-Laplacian; Asymptotic formula; Asymptotics; Conductivity distributions; Conductivity imaging; Coupling impedances; Elastic perturbations; Electrical impedance tomography; Electrical measurement; Energy density; Measured data; Non linear PDE; Numerical example; Algorithms; Diagnostic radiography; Electric impedance measurement; Electric impedance tomography; Perturbati
Tissue harmonics cancellation using time-reversal Couture, O., J.-F. Aubry, G. Montaldo, M. Tanter, and M. Fink Proceedings - IEEE Ultrasonics Symposium, 1104-1107 (2008) Résumé: Pulse-inversion sequences are sensitive to the nonlinear echoes from microbubbles allowing an improvement in the bloodto- tissue contrast. However, at larger mechanical indexes, this contrast is reduced by harmonics produced during nonlinear propagation. A method for tissue harmonics cancellation exploiting time-reversal is experimentally implemented using a 128-channel 12-bit emitter-receiver. The probe calibration is performed by acquiring the nonlinear echo of a wire in water. These distorted pulses are time-reversed, optimized and used for the pulse-inversion imaging of a tissue phantom. Compared to normal (straight) pulses, the time-reversed distorted pulses reduced the tissue signal in pulse-inversion by 11 dB. The second harmonics signal from microbubbles flowing in a wall-less vessel was unaffected by the correction. This technique can thus increase the blood-to-tissue contrast ratio while keeping the pressure and the number of pulses constant. ©2008 IEEE. Mots-clés: Cancellation; Nonlinear propagation; Pulseinversion; Tissue harmonics; Cancellation; Contrast ratio; Mechanical indexes; Microbubbles; Nonlinear propagation; Probe calibration; Pulseinversion; Second harmonics; Time-reversal; Time-reversed; Tissue harmonic; Tissue harmonics; Tissue phantom; Tissue signals; Harmonic analysis; Tissue
Tactile touch plate with variable boundary conditions Ing, R. K., D. Cassereau, M. Fink, and J.-P. Nikolovski Proceedings - European Conference on Noise Control, 4225-4229 (2008) Résumé: The touch screen device is becoming more and more widespread because it is a very user friendly human/machine interface. In acoustic domains, several approaches are used to realize such a device. Triangulation or Rayleigh waves absorption are such classical methods. However, these approaches are limited because they need a large number of sensors and are only applicable to plates of constant thickness and homogeneous materials. To remedy these limitations, a new approach is proposed using only two sensors. In this approach, one sensor is used to excite the plate, either continuously or impulsively. The second sensor is used to detect the acoustic waves generated in the plate. When a human finger comes into contact with the plate, some acoustic wave characteristics change. These changes affect different frequencies and depend on the position of the contact point. Comparing these changes with pre-recorded values, it is possible to achieve a tactile touch device that only responds to specific touch locations. Mots-clés: Acoustic domains; Classical methods; Constant thickness; Different frequency; Homogeneous materials; Human/machine interfaces; Variable boundary conditions; Wave characteristics; Acoustics; Sensors; Acoustic noise
Molecular focusing of high-intensity ultrasound Time-reversal focusing applied to targeted ultrasound contrast agents Couture, O., J.-F. Aubry, M. Tanter, and M. Fink Proceedings - IEEE Ultrasonics Symposium, 455-458 (2008) Résumé: Targeted microbubbles bind specifically to molecular of diseases and their unique acoustic signature is used to cellular processes in-vivo. The ability of time reversal to focus waves through heterogeneities on such microbubbles is demonstrated. For this purpose, were deposited on a gelatin phantom and theirsignal was recorded by a high intensity ultrasonic array. amplified time-reversed signal was reemitted and shown to back in the region where the bound microbubbles were . This proof of concept emphasizes that molecular-timereversal could guide energy deposition on early, diffuse metastatic disease.1 ©2008 IEEE. Mots-clés: Contrast agents; HIFU; Imaging; Molecular; Targeted; Ultrasound therapy; Contrast agents; HIFU; Imaging; Molecular; Targeted; Ultrasound therapy; Acoustic fields; Acoustic waves; Ultrasonics; Ultrasonic imaging
Suppression of tissue harmonics for pulse-inversion contrast imaging using time reversal Couture, O., J.-F. Aubry, G. Montaldo, M. Tanter, and M. Fink Physics in Medicine and Biology 53, no. 19, 5469-5480 (2008) Résumé: Pulse-inversion (PI) sequences are sensitive to the nonlinear echoes from microbubbles allowing an improvement in the blood-to-tissue contrast. However, at larger mechanical indices, this contrast is reduced by harmonics produced during nonlinear propagation. A method for tissue harmonics cancellation exploiting time reversal is experimentally implemented using a 128-channel 12-bit emitter receiver. The probe calibration is performed by acquiring the nonlinear echo of a wire in water. These distorted pulses are time-reversed, optimized and used for the PI imaging of a tissue phantom. Compared to normal (straight) pulses, the time-reversed distorted pulses reduced the tissue signal in PI by 11 dB. The second harmonic signals from microbubbles flowing in a wall-less vessel were unaffected by the correction. This technique can thus increase the blood-to-tissue contrast ratio while keeping the pressure and the number of pulses constant. © 2008 Institute of Physics and Engineering in Medicine. Mots-clés: Blood; Harmonic analysis; Nuclear physics; Quantum theory; Contrast imaging; Contrast ratio; Mechanical indexes; Micro-bubbles; Nonlinear echoes; Nonlinear propagations; Probe calibration; Second harmonic signals; Time reversal; Time-reversed; Tissue phantoms; Tissue; article; calibration; contrast radiography; image quality; imaging system; mathematical model; microbubble; priority journal; pulse inversion; Artifacts; Calibration; Contrast Media; Copper; Microbubbles; Phantoms, Imaging; Time Fa
Assessment of the mechanical properties of the musculoskeletal system using 2-D and 3-D very high frame rate ultrasound Deffieux, T., J.-L. Gennisson, M. Tanter, and M. Fink IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 55, no. 10, 2177-2190 (2008) Résumé: One of the great challenges for understanding muscular diseases is to assess noninvasively the active and passive mechanical properties of the musculoskeletal system. In this paper we report the use of ultrafast ultrasound imaging to explore with a submillimeter resolution the behavior of the contracting tissues in vivo (biceps brachii). To image the contraction, which is a very brief phenomenon (<100 ms), a recently designed ultrasound scanner prototype able to take up to 6000 frames/s was used. A very high frame rate from 1000 to 2500 frames/s was used to image the cross section plane of the muscle (transverse to fibers) enabling us to catch in real time the muscle contraction during a transient electrostimulation. Tissue velocities were obtained from radio frequency-based speckle tracking techniques and their profiles are discussed with respect to electrostimulation intensities and pulse repetition frequencies for different volunteers. Three-dimensional (3-D) very high frame rate movies were also acquired by repeating the experiment for different acquisition planes while triggering the imaging system with the electrostimulation device. The reconstructed 3-D velocity field allows the full localization of the contracting fibers bundle. This ultrasound technique, referred to as echo mechanomyography, offers new perspectives for in vivo and in situ noninvasive muscle diagnosis of an active contractile tissue. © 2008 IEEE. Mots-clés: Acoustic waves; Biomechanics; Fibers; Mechanical properties; Muscle; Musculoskeletal system; Optoelectronic devices; Shrinkage; Three dimensional; Ultrasonic applications; Ultrasonics; Biceps brachii; Cross section planes; Electrostimulation; High frame rates; In-situ; In-vivo; Mechanomyography; Muscle contractions; Noninvasive; Pulse Repetition frequencies; Radio frequencies; Real times; Speckle tracking techniques; Submillimeter resolutions; Tissue velocities; Ultrafast; Ultrasound imaging; Ul
Fourth-order shear elastic constant assessment in quasi-incompressible soft solids ŕnier, M., J.-L. Gennisson, C. Barrìre, D. Royer, and M. Fink. Applied Physics Letters 93, no. 10 (2008) Résumé: In isotropic quasi-incompressible media, an expression of the elastic energy density has been developed as a function of the second-, third-, and fourth-order elastic constants (respectively μ, A, D). Thus the shear nonlinearity parameter ΒS depends only on these coefficients. In this letter ΒS is measured using finite amplitude plane shear waves in agar-gelatin based phantoms. Combining the results with recently published measurements of μ and A on the same phantoms, the fourth-order shear elastic constant D is found to be of the order of 10 kPa and thus of the same order of magnitude as μ and A. © 2008 American Institute of Physics. Mots-clés: Incompressible flow; Elastic energy density; Non-linearity parameter; Soft solids; Elastic constants
High resolution MR-Elastography: A unique tool to study the rheological properties of tissue in vivo and the origin of its multiscale behaviour Larrat, B., M. Tanter, M. Fink, and R. Sinkus AIP Conference Proceedings 1027, 606-608 (2008) Résumé: Although the rheology of soft tissue samples is subject to extensive studies, mainly via rheometer measurements, only a few papers discuss the mechanical behaviour of living biological tissues. This is mainly due to the lack of a reliable and accurate technique to quantitatively assess the stress-strain relationship in vivo. In this study, we show that MR-Elastography with its full 3D potential gives unique access to the frequency dependency of the complex shear modulus. In-vivo multi-frequent experiments were conducted in rat brain, fibrotic rat liver and human breast tissue. Additionally, a full physically-motivated model, in agreement with the causality principle, has been developed to explain the observed dispersion properties and finite element simulations were conducted to understand their microscopic origin. MR-Elastography can be efficiently used to study rheology in vivo. The frequency behaviour of the macroscopic viscoelastic parameters gives additional information about the microscopic structure of the material. The observed power-law leads to the hypothesis that an underlying self-similar network is responsible for it. Simulations show that the vascular network is a potential candidate. If proven, this could lead to a contrast provided on a macroscopic scale sensitive to changes on the level of the microscopic vascular architecture. Furthermore, at low frequency, the apparent loss modulus seems to originate from the multiple scattering at the micro level rather than from the intrinsic viscosity. © 2008 American Institute of Physics. Mots-clés: Causality; MR-Elastography; Multiple scattering; Power-law; Rheology of tissues; Shear waves
Quantitative Assessment of Breast Lesion Viscoelasticity: Initial Clinical Results Using Supersonic Shear Imaging Tanter, M., J. Bercoff, A. Athanasiou, T. Deffieux, J.-L. Gennisson, G. Montaldo, M. Muller, A. Tardivon, and M. Fink Ultrasound in Medicine and Biology 34, no. 9, 1373-1386 (2008) Résumé: Abtract. This paper presents an initial clinical evaluation of in vivo elastography for breast lesion imaging using the concept of supersonic shear imaging. This technique is based on the combination of a radiation force induced in tissue by an ultrasonic beam and an ultrafast imaging sequence capable of catching in real time the propagation of the resulting shear waves. The local shear wave velocity is recovered using a time-offlight technique and enables the 2-D mapping of shear elasticity. This imaging modality is implemented on a conventional linear probe driven by a dedicated ultrafast echographic device. Consequently, it can be performed during a standard echographic examination. The clinical investigation was performed on 15 patients, which corresponded to 15 lesions (4 cases BI-RADS 3, 7 cases BI-RADS 4 and 4 cases BI-RADS 5). The ability of the supersonic shear imaging technique to provide a quantitative and local estimation of the shear modulus of abnormalities with a millimetric resolution is illustrated on several malignant (invasive ductal and lobular carcinoma) and benign cases (fibrocystic changes and viscous cysts). In the investigated cases, malignant lesions were found to be significantly different from benign solid lesions with respect to their elasticity values. Cystic lesions have shown no shear wave propagate at all in the lesion (because shear waves do not propage in liquid). These preliminary clinical results directly demonstrate the clinical feasibility of this new elastography technique in providing quantitative assessment of relative stiffness of breast tissues. This technique of evaluating tissue elasticity gives valuable information that is complementary to the B-mode morphologic information. More extensive studies are necessary to validate the assumption that this new mode potentially helps the physician in both false-positive and false-negative rejection. (E-mail: ). © 2008 World Federation for Ultrasound in Medicine & Biology. Mots-clés: Acoustic radiation force; Breast; Cancer; Elastography; Shear wave imaging; Ultrasound; Acoustic radiation force; BI-RADS; Breast; Breast lesions; Breast tissues; Cancer; Clinical evaluation; Clinical feasibility; Clinical investigation; Elasticity values; Elastography; Imaging modalities; In-vivo; Linear probing; Local estimation; Malignant lesions; Quantitative assessments; Radiation force; Real time; Relative stiffness; Shear elasticity; Shear modulus; Shear wave imaging; Shear wave velocitie
Characterization of an elastic target in a shallow water waveguide by decomposition of the time-reversal operator Philippe, F. D., C. Prada, J. De Rosny, D. Clorennec, J.-G. Minonzio, and M. Fink Journal of the Acoustical Society of America 124, no. 2, 779-787 (2008) Résumé: This paper reports the results of an investigation into extracting of the backscattered frequency signature of a target in a waveguide. Retrieving the target signature is difficult because it is blurred by waveguide reflections and modal interference. It is shown that the decomposition of the time-reversal operator method provides a solution to this problem. Using a modal theory, this paper shows that the first singular value associated with a target is proportional to the backscattering form function. It is linked to the waveguide geometry through a factor that weakly depends on frequency as long as the target is far from the boundaries. Using the same approach, the second singular value is shown to be proportional to the second derivative of the angular form function which is a relevant parameter for target identification. Within this framework the coupling between two targets is considered. Small scale experimental studies are performed in the 3.5 MHz frequency range for 3 mm spheres in a 28 mm deep and 570 mm long waveguide and confirm the theoretical results. © 2008 Acoustical Society of America. Mots-clés: Waveguides; Experimental studies; Form function; Frequency ranging; Modal interference; Second derivatives; Shallow water waveguides; Singular values; Small scale; Target identification; Target signatures; Time-reversal operator; Waveguide geometry; Targets; water; article; decomposition; elasticity; frequency analysis; geometry; priority journal; theoretical study; waveform; Acoustics; Elasticity; Models, Theoretical; Motion; Sound; Sound Spectrography; Steel; Surface Properties; Time Factors;
Measurement of shear elastic moduli in quasi-incompressible soft solids Rénier, M., J.-L. Gennisson, C. Barrière, S. Catheline, M. Tanter, D. Royer, and M. Fink AIP Conference Proceedings 1022, 303-306 (2008) Résumé: Recently a nonlinear equation describing the plane shear wave propagation in isotropic quasi-incompressible media has been developed using a new expression of the strain energy density, as a function of the second, third and fourth order shear elastic constants (respectively μ, A, D) [1]. In such a case, the shear nonlinearity parameter βs depends only from these last coefficients. To date, no measurement of the parameter D have been carried out in soft solids. Using a set of two experiments, acoustoelasticity and finite amplitude shear waves, the shear elastic moduli up to the fourth order of soft solids are measured. Firstly, this theoretical background is applied to the acoustoelasticity theory, giving the variations of the shear wave speed as a function of the stress applied to the medium. From such variations, both linear (μ) and third order shear modulus (A) are deduced in agar-gelatin phantoms. Experimentally the radiation force induced by a focused ultrasound beam is used to generate quasi-plane linear shear waves within the medium. Then the shear wave propagation is imaged with an ultrafast ultrasound scanner. Secondly, in order to give rise to finite amplitude plane shear waves, the radiation force generation technique is replaced by a vibrating plate applied at the surface of the phantoms. The propagation is also imaged using the same ultrafast scanner. From the assessment of the third harmonic amplitude, the nonlinearity parameter βS is deduced. Finally, combining these results with the acoustoelasticity experiment, the fourth order modulus (D) is deduced. This set of experiments provides the characterization, up to the fourth order, of the nonlinear shear elastic moduli in quasi-incompressible soft media. Measurements of the A moduli reveal that while the behaviors of both soft solids are close from a linear point of view, the corresponding nonlinear moduli A are quite different. In a 5% agar-gelatin phantom, the fourth order elastic constant D is found to be 30±10kPa. © 2008 American Institute of Physics. Mots-clés: Acoustoelasticity; Nonlinear shear elastic waves; Nonlinearity parameter; Soft solids; Third harmonic measurements
Eigenvalue distributions of correlated multichannel transfer matrices in strongly scattering systems Sprik, R., A. Tourin, J. De Rosny, and M. Fink Physical Review B - Condensed Matter and Materials Physics 78, no. 1 (2008) Résumé: We experimentally study the effects of correlations in the propagation of ultrasonic waves in water from a multielement source to a multielement detector through a strongly scattering system of randomly placed vertical rods. Due to the strong scattering, the wave transport in the sample is in the diffusive regime. The correlation between the waves is induced when the distance between transducer elements is within the coherence region of the scattered sound. We measure the multichannel transfer matrix H, each element of which represents the signal strength between the m individual transmitters and n receivers. The observed eigenvalue distribution of the matrix H H† clearly shows the effect of correlations between channels and can be interpreted using random matrix theory. These results are of practical importance in many areas, e.g., for evaluating the information transfer capacity of such a complex scattering system. © 2008 The American Physical Society.
Time-reversal acoustics Fink, M. Journal of Physics: Conference Series 118, no. 1 (2008) Résumé: Time-reversal mirrors (TRMs) refocus an incident acoustic field to the position of the original source regardless of the complexity of the propagation medium. TRM's have now been implemented in a variety of physical scenarios from MHz ultrasonics with order centimeter aperture size to hundreds/thousands of Hz in ocean acoustics with order hundred meter aperture size. Common to this broad range of scales is a remarkable robustness exemplified by observations at all scales that the more complex the medium between the probe source and the TRM, the sharper the focus. The relation between the medium complexity and the size of the focal spot is studied in this paper. It is certainly the most exciting property of TRM compared to standard focusing devices. A TRM acts as an antenna that uses complex environments to appears wider than it is, resulting for a broadband pulse in a refocusing quality that does not depend of the TRM aperture. In this paper, we investigate the time-reversal approach in various media of increasing complexity and we discuss the link existing between time-reversal approach and local helioseismology where Green's functions can be extracted from diffusive noise. © 2008 IOP Publishing Ltd.
Transcostal high-intensity-focused ultrasound: Ex vivo adaptive focusing feasibility study Aubry, J.-F., M. Pernot, F. Marquet, M. Tanter, and M. Fink Physics in Medicine and Biology 53, no. 11, 2937-2951 (2008) Résumé: Ex vivo experiments have been conducted through excised pork rib with bone, cartilage, muscle and skin. The aberrating effect of the ribcage has been experimentally evaluated. Adaptive ultrasonic focusing through ribs has been studied at low power. Without any correction, the pressure fields in the focal plane were both affected by inhomogeneous attenuation and phase distortion and three main effects were observed: a mean 2 mm shift of the main lobe, a mean 1.25 mm spreading of the half width of the main lobe and up to 20 dB increase of the secondary lobe level. Thanks to time-reversal focusing, a 5 dB decrease in the secondary lobes was obtained and the ratio between the energy deposited at the target location and the total amount of energy emitted by the therapeutic array was six times higher than that without correction. Time-reversal minimizes the heating of the ribs by automatically sonicating between the ribs, as demonstrated by temperature measurements using thermocouples placed at different locations on the ribcage. It is also discussed how this aberration correction process could be achieved non-invasively for clinical application. © 2008 Institute of Physics and Engineering in Medicine. Mots-clés: Decision making; Drug therapy; Focusing; Health; Heating; Photoacoustic effect; Planning; Resource allocation; Technology; Temperature measurement; Tissue engineering; Ultrasonics; (e ,3e) process; (p ,p ,t) measurements; Aberration corrections; Adaptive focusing; Clinical applications; Energy deposited; Ex-vivo; Feasibility studies; Focal planes; Focused ultrasound (FUS); half widths; Inhomogeneous attenuation; Institute of Physics; low powers; Main effects; phase distortions; Pressure fields;
Characterization of an elastic cylinder and an elastic sphere with the time-reversal operator: Application to the sub-resolution limit Minonzio, J.-G., F. D. Philippe, C. Prada, and M. Fink Inverse Problems 24, no. 2 (2008) Résumé: The Décomposition de l'Opérateur de Retournement Temporel method applies to scattering analysis with arrays of transducers. It comprises the study of the time-reversal invariants which correspond to the eigenvectors of the time-reversal operator or to the singular vectors of the array response matrix K. In this paper, the decomposition of the scattered pressure into normal modes of vibrations is used to determine the theoretical time-reversal invariants for a large elastic object such as a cylinder or sphere. For an N transducers one-dimensional array, the time-reversal operator is dimension N. It is shown that the dimension is reduced to 2k0a for a cylinder or a sphere, where a is the scatterer radius and k0 is the wave number in the surrounding fluid. Furthermore, this approach provides analytical expressions of symmetric and anti-symmetric singular values and vectors in the sub-resolution limit, i.e. when the scatterer diameter is smaller than the array resolution cell. These results are verified experimentally and in good agreement with the original point of view: for a small scatterer, one singular value dominates and the associated singular vector focuses isotropically on the scatterer. © 2008 IOP Publishing Ltd. Mots-clés: Eigenvalues and eigenfunctions; Electromagnetic wave scattering; Matrix algebra; Transducers; Vectors; Elastic cylinders; Elastic sphere; Mathematical operators
Potential of MRI and ultrasound radiation force in elastography: Applications to diagnosis and therapy Sinkus, R., M. Tanter, J. Bercoff, K. Siegmann, M. Pernot, A. Athanasiou, and M. Fink Proceedings of the IEEE 96, no. 3, 490-499 (2008) Résumé: Elastography has many exciting new areas of application in the domains of diagnosis and therapy. We present in this overview the current gold standard given by MR elastography, which uses a full three-dimensional approach to solve locally for the unknown complex shear modulus at one frequency. Clinical results for benign and malignant breast lesions are shown. Less rigorous in terms of data completeness, but significantly faster and easier to apply, we introduce the ultrasound-based supersonic shear imaging technique, which uses acoustic radiation force to generate inside the medium planar shear waves. Subsequent ultrafast imaging of the propagating shear wave allows one to recuperate detailed time-of-flight maps of in-vivo breast lesions. Lastly, we present initial results for using magnetic resonance imaging and acoustic radiation force together for high-intensity focused ultrasound interventions. © 2006 IEEE. Mots-clés: Acoustic radiation force; Elastography; High-intensity focused ultrasound (HIFU); Magnetic resonance imaging (MRI); Supersonic shear imaging; Ultrasound; Acoustic radiation force; Elastography; High-intensity focused ultrasound (HIFU); Supersonic shear imaging; Ultrasound; Acoustic emissions; Acoustic radiators; Acoustic wave propagation; Gold compounds; Magnetic resonance; Magnetic resonance imaging; Shear waves; Sonochemistry; Three dimensional; Ultrasonic applications; Ultrasonic transmission
Green's function estimation in speckle using the decomposition of the time reversal operator: Application to aberration correction in medical imaging Robert, J.-L., and M. Fink Journal of the Acoustical Society of America 123, no. 2, 866-877 (2008) Résumé: The FDORT method (French acronym for decomposition of the time reversal operator using focused beams) is a time reversal based method that can detect point scatterers in a heterogeneous medium and extract their Green's function. It is particularly useful when focusing in a heterogeneous medium. This paper generalizes the theory of the FDORT method to random media (speckle), and shows that it is possible to extract Green's functions from the speckle signal using this method. Therefore it is possible to achieve a good focusing even if no point scatterers are present. Moreover, a link is made between FDORT and the Van Cittert-Zernike theorem. It is deduced from this interpretation that the normalized first eigenvalue of the focused time reversal operator is a well-known focusing criterion. The concept of an equivalent virtual object is introduced that allows the random problem to be replaced by an equivalent deterministic problem and leads to an intuitive understanding of FDORT in speckle. Applications to aberration correction are presented. The reduction of the variance of the Green's function estimate is discussed. Finally, it is shown that the method works well in the presence of strong interfering scatterers. © 2008 Acoustical Society of America. Mots-clés: Aberrations; Medical imaging; Problem solving; Speckle; Theorem proving; FDORT method; Time reversal operators; Green's function; article; decomposition; imaging system; mathematical model; methodology; priority journal; radiation scattering; signal detection; theory; Algorithms; Computer Simulation; Fourier Analysis; Humans; Image Enhancement; Interferometry; Models, Theoretical; Phantoms, Imaging; Rubber; Ultrasonography; User-Computer Interface
Focusing properties of near-field time reversal De Rosny, J., and M. Fink Physical Review A - Atomic, Molecular, and Optical Physics 76, no. 6 (2007) Résumé: A time-reversal mirror (TRM) is a plane apparatus that generates the time symmetric of a wave produced by an initial source. Here we look for the conditions to obtain subwavelength focusing when the initial source is in the near field of the TRM and the propagating medium is homogeneous and isotropic. Three variants of TRM are studied: TRM made of monopoles, dipoles, or both of them. The analysis is performed in terms of evanescent and propagative waves. We conclude that only the dipole-TRM leads to subwavelength focusing. © 2007 The American Physical Society. Mots-clés: Focusing; Mirrors; Wave propagation; Wavelength; Near-field time reversal; Propagative waves; Subwavelength focusing; Time symmetric; Time and motion study
MR elastography of breast lesions: Understanding the solid/liquid duality can improve the specificity of contrast-enhanced MR mammography Sinkus, R., K. Siegmann, T. Xydeas, M. Tanter, C. Claussen, and M. Fink Magnetic Resonance in Medicine 58, no. 6, 1135-1144 (2007) Résumé: The purpose of this analysis is to explore the potential diagnostic gain provided by the viscoelastic shear properties of breast lesions for the improvement of the specificity of contrast enhanced dynamic MR mammography (MRM). The assessment of viscoelastic properties is done via dynamic MR elastography (MRE) and it is demonstrated that the complex shear modulus of in vivo breast tissue follows within the frequency range of clinical MRE a power law behavior. Taking benefit of this frequency behavior, data are interpreted in the framework of the exact model for wave propagation satisfying the causality principle. This allows to obtain the exponent of the frequency power law from the complex shear modulus at one single frequency which is validated experimentally. Thereby, scan time is drastically reduced. It is observed that malignant tumors obtain larger exponents of the power law than benign tumors indicating a more liquid-like behavior. The combination of the Breast Imaging Reporting and Data System (BIRADS) categorization obtained via MRM with viscoelastic information leads to a substantial rise in specificity. Analysis of 39 malignant and 29 benign lesions shows a significant diagnostic gain with an increase of about 20% in specificity at 100% sensitivity. © 2007 Wiley-Liss, Inc. Mots-clés: Breast cancer; Frequency power law behavior; MR elastography; MR mammography; Rheology; gadolinium pentetate; adult; aged; article; breast lesion; clinical article; controlled study; elastography; female; human; imaging system; mammography; medical instrumentation; nuclear magnetic resonance; sensitivity and specificity; viscoelasticity; Breast Neoplasms; Contrast Media; Elasticity Imaging Techniques; Female; Gadolinium DTPA; Humans; Image Enhancement; Image Interpretation, Computer-Assisted; Ma
Acoustoelasticity in soft solids: Assessment of the nonlinear shear modulus with the acoustic radiation force Gennisson, J.-L., M. Rénier, S. Catheline, C. Barrière, J. Bercoff, M. Tanter, and M. Fink Journal of the Acoustical Society of America 122, no. 6, 3211-3219 (2007) Résumé: The assessment of viscoelastic properties of soft tissues is enjoying a growing interest in the field of medical imaging as pathologies are often correlated with a local change of stiffness. To date, advanced techniques in that field have been concentrating on the estimation of the second order elastic modulus (μ). In this paper, the nonlinear behavior of quasi-incompressible soft solids is investigated using the supersonic shear imaging technique based on the remote generation of polarized plane shear waves in tissues induced by the acoustic radiation force. Applying a theoretical approach of the strain energy in soft solid [Hamilton, J. Acoust. Soc. Am. 116, 41-44 (2004)], it is shown that the well-known acoustoelasticity experiment allowing the recovery of higher order elastic moduli can be greatly simplified. Experimentally, it requires measurements of the local speed of polarized plane shear waves in a statically and uniaxially stressed isotropic medium. These shear wave speed estimates are obtained by imaging the shear wave propagation in soft media with an ultrafast echographic scanner. In this situation, the uniaxial static stress induces anisotropy due to the nonlinear effects and results in a change of shear wave speed. Then the third order elastic modulus (A) is measured in agar-gelatin-based phantoms and polyvinyl alcohol based phantoms. © 2007 Acoustical Society of America. Mots-clés: Elastic moduli; Elasticity; Medical imaging; Nonlinear analysis; Pathology; Shear waves; Tissue; Acoustic radiation forces; Acoustoelasticity experiments; Shear wave propagation; Soft solids; Acoustic radiators; agar; polyvinyl alcohol; acoustics; anisotropy; article; elasticity; imaging; nonlinear system; phantom; physical chemistry; priority journal; radiation energy; radiodiagnostic equipment and supplies; shear strength; solid; ultrasound; young modulus; Agar; Animals; Anisotropy; Connective
Anisotropic viscoelastic properties of the corpus callosum - Application of high-resolution 3D MR-elastography to an Alzheimer mouse model Larrat, B., Q. C. Chan, X. F. Yang, G. Li, E. S. Yang, M. Fink, and R. Sinkus Proceedings - IEEE Ultrasonics Symposium, 676-679 (2007) Résumé: Alzheimer's disease (AD) is characterized by progressive cognitive deterioration together with declining activities of daily living and neuropsychiatric symptoms. It is the most common cause of dementia. It is recognized that the production and maintenance of myelin is essential for normal brain function. Aging-related breakdown of myelin negatively impacts the cognitive performances with the neurofibrilary tangles and amyloid plaques being the hallmarks of the disease. Nowadays, the only definite way to diagnose AD is to find out whether there are plaques and tangles in brain tissue. This requires histopathological examination of brain tissue. Previous researches on AD using MRI mainly focus on direct plaque imaging. This study aims to validate the hypothesis that AD alters the mechanical properties of the axons in the region between hippocampus and cortex, i.e. within the Corpus Callosum (CC) which is an area strongly affected by demvelination. As a unique tool to study non-invasively those properties, we use 3D MR-elastography operating at 1000Hz mechanical excitation frequency. Post-processing of the complex-valued displacement field provides the local fiber direction (determined by two Euler angles) and two complex shear moduli: one perpendicular to the local fiber direction and one parallel to it. Each modulus is a complex number giving access to both the anisotropic elasticity μ and viscosity η. The displacement fields are measured at an isotropic resolution of 300μm. Four transgenic female mice expressing mutant human APP/PS1 genes and three wild-type (WT) control mice were studied over several weeks. We observe locally enhanced elasticity and viscosity in the corpus callosum compared to the rest of the brain. As expected from normal anatomy, this region also shows a significantly higher anisotropy (μ ∥- μ ⊥ characterizing the transversal isotropic mechanical properties of this white matter region. The AD group shows a decrease in both μ ∥ and μ ⊥. It also seems to have a decreased value of perpendicular viscosity suggesting easier wave propagation in the transverse direction due to demyelination. Those preliminary results indicate that AD alters the mechanical properties of the white matter. Those differences were not detectable when utilizing an isotropic model for the reconstruction of the viscoelastic properties. © 2007 IEEE. Mots-clés: Alzheimer's disease; Anisotropy; Corpus callosum; Demyelination; Magnetic resonance elastography; Viscoelastic properties; White matter; Anisotropy; Arsenic; Biomechanics; Brain; Chlorine compounds; Crystallography; Elasticity; Fiber optics; Hydrodynamics; Three dimensional; Three dimensional computer graphics; Ultrasonics; Viscosity; Activities of daily living; Alzheimer; Alzheimer's disease; Amyloid plaques; Anisotropic elasticity; Brain functions; Brain tissues; Complex numbers; Corpus callos
Active and passive muscle properties assessed by ultrasound techniques Deffieux, T., J.-L. Gennisson, G. Montaldo, M. Tanter, and M. Fink Proceedings - IEEE Ultrasonics Symposium, 668-671 (2007) Résumé: The non invasive and in vivo assessment of the active and passive properties of the musculoskeletal system remains today a great challenge for the understanding of muscular diseases. In a previous paper [1], we showed that the transient contraction of a muscle fiber bundle triggered by electrostimulation can be followed in space and time by an ultrafast ultrasound system. On the one hand, this experiment is generalized to measure the three dimensional (3D) velocity fields allowing a much easier localization of the contracting fibers bundle. On the other hand, the supersonic shear imaging technique is applied to assess viscoelastic properties of the biceps brachü in different conditions. By combining in vivo imaging of both passive and active muscle activity, this study aim to provide new potential ultrasonic tools for muscle diseases diagnosis and monitoring. In order to image the contraction, which is a very quick phenomenon, an ultrasound scanner able to take up to 5000 frames/s was used. Tissue velocities were obtained from conventional speckle tracking techniques. The probe, positioned perpendicularly to the arm in a water tank, was moved with a linear motor. For each position, the imaging system was set to trigger an electrostimulation firing the contraction. A second experiment for the assessment of passive muscle elastic properties in different positions of the arm and contraction levels is then performed using the same probe in the supersonic shear imaging (SSI) mode. Generated by the radiation force induced by a focused ultrasound beam, shear waves propagate in the medium and are imaged by an ultrafast ultrasound scanner allowing the reconstruction of viscoelastic properties. The localization of the contracting fibers bundle and the resolution of its main temporal and spatial behavior are demonstrated. Paving the way to a clinical protocol on muscle diseases, viscoelastic parameters are measured in different conditions and reproducibility is discussed. These two complementary ultrasound techniques offer new perspectives for muscle diagnosis both as an active contractile tissue and as a passive tissue. © 2007 IEEE. Mots-clés: Dispersion; In vivo muscle contraction; Muscle elasticity; Passive and active properties of the muscle; Supersonic shear imaging; Ultrafast ultrasonic imaging; Acoustic waves; Experiments; Fiber optics; Fibers; Imaging systems; Imaging techniques; Joints (anatomy); Musculoskeletal system; Optoelectronic devices; Scanning; Shrinkage; Space probes; Three dimensional; Ultrasonic applications; Ultrasonic imaging; Ultrasonic transmission; Ultrasonics; Water tanks; Dispersion; Elastic properties; Elec
Full 3D inversion of the viscoelasticity wave propagation problem for 3D ultrasound elastography in breast cancer diagnosis Muller, M., J.-L. Gennisson, T. Deffieux, R. Sinkus, P. Annic, G. Montaldo, M. Tanter, and M. Fink Proceedings - IEEE Ultrasonics Symposium, 672-675 (2007) Résumé: An experimental 3D Ultrasound Elastography setup has been designed for breast cancer diagnosis improvement. 3D Elastography assessment is generally based on the combination of adjacent 2D elasticity maps, obtained through simple 2D inverse problem resolution. Meanwhile, 3D sonoelastography is based on simple inversion approaches to the viscoelasticity problem. The system presented here is based on the resolution of a full 3D inverse problem, from the complete ultrasound-based measurement of the three components of the 3D displacement field. The 3D information considerably improves the accuracy and reliability of the quantitative measurements and circumvents the operator-dependent aspects of 2D echography diagnosis. The combination of 3D echography and elastography could be a very promising tool for in vivo breast cancer diagnosis. The X-ray system of a commercial mammographie bed was replaced by an ultrasound device. Shear waves were generated using a low frequency vibrator. Resulting displacements in tissues were imaged using an echographic probe moving stepwise around the breast. Advanced techniques such as compounding echographic probe sub-apertures and 2D vector Doppler algorithms were used to assess the three components of the displacement. Shear elasticity, viscosity and anisotropy were quantified using a 3D elastic properties reconstruction algorithm. A 3D finite difference simulation algorithm based on the viscoelastic propagation equation was used to model the 3D forward problem, and validate the inverse reconstruction algorithm. Simulated displacements in a numerical phantom were used as inputs for the inverse problem resolution, allowing the reconstruction of elastic properties similar to that of the numerical phantom. Similarly to MR-Elastography, the inverse problem was solved in the Fourier domain. However, overcoming the data acquisition limitations of MR-Elastography, the ultrasound-based approach enables the implementation of frequency compound methods based on averaging the data at different shear frequencies, increasing the measurement accuracy. In the present study, the experimental setup was optimized using numerical simulations and validated in vitro. In vitro experiments were conducted on a calibrated phantom exhibiting harder inclusions. Its 3D elastic properties were reconstructed and found consistent with that given by the manufacturer. This study allowed the numerical and experimental validation of the complete 3D Elastography protocol. © 2007 IEEE. Mots-clés: 3D elastography; Full in verse problem; Ultrafast imaging; Acoustic waves; Arsenic compounds; Chlorine compounds; Computer simulation; Crack propagation; Crystallography; Data acquisition; Difference equations; Differentiation (calculus); Elasticity; Finite difference method; Inverse problems; Laws and legislation; Maps; Mathematical operators; Numerical analysis; Optical systems; Repair; Restoration; Three dimensional; Tissue engineering; Ultrasonic imaging; Ultrasonics; Viscoelasticity; Viscos
Optimal adaptive focusing through heterogeneous media with the minimally invasive inverse filter Vignon, F., J. De Rosny, J.-F. Aubry, and M. Fink Journal of the Acoustical Society of America 122, no. 5, 2715-2724 (2007) Résumé: The inverse filter is a technique used to adaptively focus waves through heterogeneous media. It is based on the inversion of the Green's functions matrix between the M transducers of a focusing array and N control points in the focal area. The inverse filter minimizes the pressure deposited around the focal point. However it is highly invasive, requiring the presence of N transducers or hydrophones in the focal area at the control points' locations to measure the Green's functions. This paper presents a way of reaching the inverse filter's focusing quality with a minimally invasive setup: only one transducer (at the desired focal location) is needed. This minimally invasive inverse filter takes advantage of the fact all the information about the propagation medium can be retrieved from the signals backscattered by the medium towards the focusing array, if the propagation medium is lossless. A numerical simulation is performed to test this minimally invasive inverse filter through a scattering, lossless medium. The focusing quality equals the conventional, highly invasive inverse filter's. The average spatial and temporal contrast is increased by up to 10 dB compared to the time reversal focusing. © 2007 Acoustical Society of America. Mots-clés: Acoustic arrays; Acoustic transducers; Acoustic waves; Computer simulation; Green's function; Hydrophones; Green's functions matrixs; Heterogeneous media; Inverse filters; Propagation medium; Adaptive filters; acoustics; article; filter; priority journal; radiation scattering; simulation; spatial discrimination; time perception; transducer
Nonlinear shear elastic moduli in quasi-incompressible soft solids Rénier, M., J.-L. Gennisson, M. Tanter, S. Catheline, C. Barrière, D. Royer, and M. Fink Proceedings - IEEE Ultrasonics Symposium, 554-557 (2007) Résumé: Dynamic elastography holds great promise for biological tissues characterization. Resulting from the radiation force induced by focused ultrasound beam, plane shear waves are generated within the medium and imaged with an ultrafast ultrasound scanner. Known as Supersonic Shear Imaging (SSI) technique, this method allows, from the measurements of shear wave velocities, to compute shear modulus (μ) maps. Beside, in order to improve tissue diagnostic, the evaluation of the nonlinear elastic moduli could be of some interest. Recently a new formulation of the nonlinear equation describing the propagation of plane shear waves in isotropic soft incompressible solids have been developed using a new expression, up to the fourth order, of the strain energy density (e): e = μI2 + A/3 I3 DI 22 Where I2, I3 are invariants defined by Landau of the strain tensor and A, D the third and fourth order shear elastic constants. It has been shown that the nonlinearity parameter depends only on three coefficients βs = βs(μ, A, D). To date, no measurement of the parameter D have been carried out in incompressible media. In order to estimate the nonlinear parameter A, this theoretical background on soft incompressible solids is applied to the acoustoelasticity theory. Such analysis gives the variations of shear wave speed as a function of the applied stress and leads to measure both the linear shear modulus (μ) and the third order shear modulus (A). Taking advantages of the SSI technique, an acoustoelasticity experiment is performed in different incompressible soft media (agar-gelatin based phantoms). In addition, to create finite amplitude plane shear waves, the SSI technique is replaced by a vibrator applied at the surface of the phantoms. Thanks to the ultrasound ultrafast imaging system, the third harmonic component is generated by nonlinearity is measured as a function of the propagation distance. Then by comparing experiments and analytical expression of the third harmonic component given by a perturbation method, the nonlinear parameter βs is deduced. Finally, the combination of these experiments with results obtained in acoustoelasticity leads to the determination of the fourth order elastic modulus (D). First, measurements of the A modulus reveal that while the behavior of phantoms is quite close from a linear point of view, their nonlinear modulus A are quite different. Applied to acoustoelasticity, the SSI technique provides potential medical applications in in vivo conditions for nonlinear characterization of biological tissues. Second, results from the complete procedure reveal a variation of the nonlinear behavior as a function of the gelatin concentration increasing. This set of experiments provides the characterization, up to the fourth order, of the nonlinear shear elastic moduli in incompressible soft media. ©2007 IEEE. Mots-clés: Acoustoelasticity; Finite amplitude shear waves; Nonlinear elasticity; Soft solids; Supersonic shear imaging; Transient elastography; Acoustic waves; Elastic waves; Health; Incompressible flow; Maps; Nonlinear equations; Shear waves; Ultrasonic applications; Ultrasonic imaging; Ultrasonics; Acoustoelasticity; Biological tissues; Elastography; Finite amplitude shear waves; Focused ultrasound; Fourth order; Incompressible solids; Nonlinear elasticity; Radiation force; Shear elastic modulus; Shear
High power phased array prototype for clinical high intensity focused ultrasound: Applications to transcostal and transcranial therapy Pernot, M., J.-F. Aubry, M. Tanter, F. Marquet, G. Montaldo, A.-L. Boch, M. Kujas, D. Seilhean, and M. Fink Annual International Conference of the IEEE Engineering in Medicine and Biology - Proceedings, 234-237 (2007) Résumé: Bursts of focused ultrasound energy three orders of magnitude more intense than diagnostic ultrasound became during the last decade a noninvasive option for treating cancer from breast to prostate or uterine fibroid. However, many challenges remain to be addressed. First, the corrections of distortions induced on the ultrasonic therapy beam during its propagation through defocusing obstacles like skull bone or ribs remain today a technological performance that still need to be validated clinically. Secondly, the problem of motion artifacts particularly important for the treatment of abdominal parts becomes today an important research topic. Finally, the problem of the treatment monitoring is a wide subject of interest in the growing HIFU community. For all these issues, the potential of new ultrasonic therapy devices able to work both in Transmit and Receive modes will be emphasized. A review of the work under achievement at L.O.A. using this new generation of HIFU prototypes on the monitoring, motion correction and aberrations corrections will be presented. © 2007 IEEE. Mots-clés: Diagnosis; Patient monitoring; Patient treatment; Ultrasonic applications; Transcranial therapy; Treatment monitoring; Biomedical engineering
Theory of the time reversal cavity for electromagnetic fields Carminati, R., R. Pierrat, J. De Rosny, and M. Fink Optics Letters 32, no. 21, 3107-3109 (2007) Résumé: We derive a general expression of the electric dyadic Green function in a time-reversal cavity, based on vector diffraction theory in the frequency domain. Our theory gives a rigorous framework to time-reversal experiments using electromagnetic waves and suggests a methodology to design structures generating subwavelength focusing after time reversal. © 2007 Optical Society of America. Mots-clés: Diffraction; Electromagnetic waves; Frequency domain analysis; Green's function; Microcavities; Time reversal cavity; Electromagnetic fields
Ultrasonic arrays: New therapeutic developments Aubry, J.-F., M. Pernot, M. Tanter, G. Montaldo, and M. Fink Journal de Radiologie 88, no. 11 C2, 1801-1809 (2007) Résumé: Bursts of focused ultrasound energy a billion times more intense than diagnostic ultrasound have become a non-invasive option for tumor ablation, from prostate cancer to uterine fibroid, during the last decade. Despite this progress, many issues still need to be addressed. First, for brain targeting, the correction of distortions induced by the skull remains today a technological achievement that still needs to be validated clinically. Secondly, the problem of motion artifacts for abdominal treatments becomes today an important research topic. For all these issues, the potential of new ultrasonic therapy devices able to work both in Transmit and Receive modes will be emphasized and clinical results on monkeys and pigs will be presented. © 2007. Éditions Françaises de Radiologie. Édité par Elsevier Masson SAS. Mots-clés: Focused Ultrasound; Motion compensation; Therapy; Time reversal; artifact; echoencephalography; human; in vitro study; in vivo study; medical instrumentation; monkey; non invasive procedure; nonhuman; nuclear magnetic resonance imaging; prostate cancer; review; simulation; skull; swine; three dimensional imaging; ultrasound; ultrasound therapy; uterus myoma; validation study; Abdomen; Animals; Artifacts; Brain; Echoencephalography; Haplorhini; Humans; Models, Animal; Models, Biological; Models,
Nonlinear shear wave interaction in soft solids Jacob, X., S. Catheline, J.-L. Gennisson, C. Barrière, D. Royer, and M. Fink Journal of the Acoustical Society of America 122, no. 4, 1917-1926 (2007) Résumé: This paper describes nonlinear shear wave experiments conducted in soft solids with transient elastography technique. The nonlinear solutions that theoretically account for plane and nonplane shear wave propagation are compared with experimental results. It is observed that the cubic nonlinearity implied in high amplitude transverse waves at f0 =100 Hz results in the generation of odd harmonics 3 f0, 5 f0. In the case of the nonlinear interaction between two transverse waves at frequencies f1 and f2, the resulting harmonics are fi ±2 fj (i,j=1,2). Experimental data are compared to numerical solutions of the modified Burgers equation, allowing an estimation of the nonlinear parameter relative to shear waves. The definition of this combination of elastic moduli (up to fourth order) can be obtained using an energy development adapted to soft solid. In the more complex situation of nonplane shear waves, the quadratic nonlinearity gives rise to more usual harmonics, at sum and difference frequencies, fi ± fj. All components of the field have to be taken into account. © 2007 Acoustical Society of America. Mots-clés: Elastic moduli; Harmonic distortion; Parameter estimation; Burgers equation; Elastography; Nonlinear interaction; Quadratic nonlinearity; Soft solids; Shear waves; acoustics; article; elasticity; elastography; energy; frequency modulation; mathematical analysis; nonlinear system; priority journal; shear rate; solid; theoretical study; young modulus; Acoustics; Anisotropy; Biomechanics; Elasticity; Finite Element Analysis; Humans; Linear Models; Models, Theoretical; Nonlinear Dynamics; Phantoms,
New devices and promising approaches for clinical H.I.F.U. applications Tanter, M., J. Aubry, M. Pernot, F. Marquet, R. Sinkus, and M. Fink AIP Conference Proceedings 911, 23-29 (2007) Résumé: Bursts of focused ultrasound energy three orders of magnitude more intense than diagnostic ultrasound became during the last decade a noninvasive option for treating cancer from breast to prostate or uterin fibroid. However, many challenges remain to be addressed. First, the corrections of distortions induced on the ultrasonic therapy beam during its propagation through defocusing obstacles like skull bone or ribs remains today a technological performance that still needs to be validated clinically. Secondly, the problem of motion artifacts particularly important for the treatment of abdominal parts becomes today an important research topic. Finally, the problem of the treatment monitoring is a wide subject of interest in the growing HIFU community. For all these issues, the potential of new ultrasonic therapy devices able to work both in Transmit and Receive modes will be emphasized. A review of the work under achievement at L.O.A. using this new generation of HIFU prototypes on the monitoring, motion and aberrations corrections problems will be presented. © 2007 American Institute of Physics. Mots-clés: Adaptive focusing; Brain therapy; Elastography; Monitoring; Motion correction; Time reversal
Non-invasive transcranial brain therapy guided by CT scans: An in vivo monkey study Marquet, F., M. Pernot, J.-F. Aubry, G. Montaldo, M. Tanter, A.-L. Boch, M. Kujas, D. Seilhean, and M. Fink AIP Conference Proceedings 911, 554-560 (2007) Résumé: Brain therapy using focused ultrasound remains very limited due to the strong aberrations induced by the skull. A minimally invasive technique using time-reversal was validated recently in-vivo on 20 sheeps. But such a technique requires a hydrophone at the focal point for the first step of the time-reversal procedure. A completely noninvasive therapy requires a reliable model of the acoustic properties of the skull in order to simulate this first step. 3-D simulations based on high-resolution CT images of a skull have been successfully performed with a finite differences code developed in our Laboratory. Thanks to the skull porosity, directly extracted from the CT images, we reconstructed acoustic speed, density and absorption maps and performed the computation. Computed wavefronts are in good agreement with experimental wavefronts acquired through the same part of the skull and this technique was validated in-vitro in the laboratory. A stereotactic frame has been designed and built in order to perform non invasive transcranial focusing in vivo. Here we describe all the steps of our new protocol, from the CT-scans to the therapy treatment and the first in vivo results on a monkey will be presented. This protocol is based on protocols already existing in radiotherapy. © 2007 American Institute of Physics. Mots-clés: 3D simulations; Adaptive focusing; Brain therapy; Non invasise
A0 mode interaction with a plate free edge: Theory and experiments at very low frequency by thickness product Ribay, G., S. Catheline, D. Clorennec, R. K. Ing, and M. Fink Journal of the Acoustical Society of America 122, no. 2, 711-714 (2007) Résumé: When a plane acoustic wave reaches a medium with an impedance infinite or null, it experiences a phase shift of zero or π and its amplitude on the edge is maximum or vanishes. The case of a flexion wave (A0 Lamb wave) at a free end is also simple; its amplitude is multiplied by a factor 22 and the phase shift is π 2. The evanescent wave at the origin of these phenomena, perfectly described by the classical flexural plate theory, is identified as the imaginary A1 mode of the exact Rayleigh-Lamb theory. The experiences confirm the theoretical predictions. © 2007 Acoustical Society of America. Mots-clés: Acoustic impedance; Phase shift; Rayleigh waves; Surface waves; Evanescent wave; Mode interaction; Plate theory; Thickness product; Acoustic waves; acoustic impedance; amplitude modulation; article; flexural plate theory; lamb wave theory; prediction; priority journal; theory; vibration; waveform; Acoustics; Fourier Analysis; Humans; Models, Theoretical; Sound; Sound Localization; Ultrasonics
Experimental detection and focusing in shallow water by decomposition of the time reversal operator Prada, C., J. De Rosny, D. Clorennec, J.-G. Minonzio, A. Aubry, M. Fink, L. Berniere, P. Billand, S. Hibral, and T. Folegot Journal of the Acoustical Society of America 122, no. 2, 761-768 (2007) Résumé: A rigid 24-element source-receiver array in the 10-15 kHz frequency band, connected to a programmable electronic system, was deployed in the Bay of Brest during spring 2005. In this 10- to 18-m -deep environment, backscattered data from submerged targets were recorded. Successful detection and focusing experiments in very shallow water using the decomposition of the time reversal operator (DORT method) are shown. The ability of the DORT method to separate the echo of a target from reverberation as well as the echo from two different targets at 250 m is shown. An example of active focusing within the waveguide using the first invariant of the time reversal operator is presented, showing the enhanced focusing capability. Furthermore, the localization of the scatterers in the water column is obtained using a range-dependent acoustic model. © 2007 Acoustical Society of America. Mots-clés: Backscattering; Data acquisition; Frequency bands; Signal receivers; Waveguide components; Acoustic model; Time reversal operator (DORT method); Water column; Water; article; decomposition; echolocation; electronics; frequency modulation; priority journal; receiver operating characteristic; sound detection; sound intensity; water content; Kinetics; Models, Theoretical; Sound; Sound Localization; Time; Water
In vivo transcranial brain surgery with an ultrasonic time reversal mirror Pernot, M., J.-F. Aubry, M. Tanter, A.-L. Boch, F. Marquet, M. Kujas, D. Seilhean, and M. Fink Journal of Neurosurgery 106, no. 6, 1061-1066 (2007) Résumé: Object. High-intensity focused ultrasonography is known to induce controlled and selective noninvasive destruction of tissues by focusing ultrasonic beams within organs, like a magnifying glass concentrating enough sunlight to burn a hole in paper. Such a technique should be highly interesting for the treatment of deep-seated lesions in the brain. Nevertheless, ultrasonic tissue ablation in the brain has long been hampered by the defocusing effect of the skull bone. Methods. In this in vivo study, the authors used a high-power time-reversal mirror specially designed for noninvasive ultrasonic brain treatment to induce thermal lesions through the skulls of 10 sheep. The sheep were divided into three groups and, depending on group, were killed 1, 2, or 3 weeks after treatment. The thermal lesions were confirmed based on findings of posttreatment magnetic resonance imaging and histological examinations. After treatment, the basic neurological functions of the animals were unchanged: the animals recovered from anesthesia without any abnormal delay and did not exhibit signs of paralysis or coma. No major behavioral change was observed. Conclusions. The results provide striking evidence that noninvasive ultrasonographic brain surgery is feasible. Thus the authors offer a novel noninvasive method of performing local brain ablation in animals for behavioral studies. This technique may lead the way to noninvasive and nonionizing treatment of brain tumors and neurological disorders by selectively targeting intracranial lesions. Nevertheless, sheep do not represent a good functional model and extensive work will need to be conducted preferably on monkeys to investigate the effects of this treatment. Mots-clés: High-intensity ultrasonography; Noninvasive surgery; Sheep; Ultrasonography; animal experiment; article; brain surgery; controlled study; device; histology; in vivo study; nonhuman; nuclear magnetic resonance imaging; priority journal; sheep; skull; thermal injury; ultrasonic time reversal mirror; ultrasound; Animals; Behavior, Animal; Brain; Feasibility Studies; Magnetic Resonance Imaging; Neurologic Examination; Neurosurgical Procedures; Sheep; Transducers; Ultrasonics
Transient optoelastography in optically diffusive media Bossy, E., A. R. Funke, K. Daoudi, A.-C. Boccara, M. Tanter, and M. Fink Applied Physics Letters 90, no. 17, 174111 (2007) Résumé: The authors present a camera-based optical detection scheme designed to detect the transient motion created by the acoustic radiation force in soft elastic media. An optically diffusive tissue-mimicking phantom was illuminated with coherent laser light, and a high speed camera (2 kHz frame rate) was used to acquire and cross-correlate consecutive speckle patterns. Time-resolved transient decorrelation of the optical speckle was measured as the result of localized motion induced by the radiation force and the associated propagating shear waves. The proposed technique is sensitive only to the low frequency transient motion induced in the medium by the radiation force. © 2007 American Institute of Physics. Mots-clés: Cameras; Image sensors; Motion estimation; Shear waves; Speckle; Tissue; Optoelastography; Radiation force; Transient decorrelation; Transient motion; Medical imaging
Imaging of optically diffusive media by use of opto-elastography Bossy, E., A. R. Funke, K. Daoudi, M. Tanter, M. Fink, and C. Boccara Progress in Biomedical Optics and Imaging - Proceedings of SPIE 6437 (2007) Résumé: We present a camera-based optical detection scheme designed to detect the transient motion created by the acoustic radiation force in elastic media. An optically diffusive tissue mimicking phantom was illuminated with coherent laser light, and a high speed camera (2 kHz frame rate) was used to acquire and cross-correlate consecutive speckle patterns. Time-resolved transient decorrelations of the optical speckle were measured as the results of localised motion induced in the medium by the radiation force and subsequent propagating shear waves. As opposed to classical acousto-optic techniques which are sensitive to vibrations induced by compressional waves at ultrasonic frequencies, the proposed technique is sensitive only to the low frequency transient motion induced in the medium by the radiation force. It therefore provides a way to assess both optical and shear mechanical properties. Mots-clés: Acousto-optic imaging; Elastography; Optical speckle; Radiation force; Acoustic wave propagation; Cameras; Motion estimation; Optical systems; Radiation; Shear waves; Acousto-optic imaging; Optical speckle; Radiation force; Imaging systems
Elastography using ultrasound or magnetic resonance: New imaging tools for cancer diagnosis Tanter, M., J. Bercoff, R. Sinkus, T. Deffieux, J.-L. Gennisson, and M. Fink Medecine Nucleaire 31, no. 4 SPEC. ISS., 132-141 (2007) Résumé: Despite recent progress, breast cancer remains today a major public health problem as it represents the main morbidity incidence for woman with 42,000 new cases and 11,600 deaths per year in France. X-Ray mammography which is the "gold standard" exam for breast screening relies on an excellent sensitivity (nevertheless its quality is varying with respect to breast density). However, its specificity for malignancy diagnosis remains moderate leading to many useless interventions for lesions proven a posteriori to be benign by histology. The other imaging techniques such as echography and magnetic resonance imaging (MRI) also possess their own limits. Echography is strongly operator-dependent. Dynamic MRI with injection of contrast agents has a high sensitivity for breast cancer detection (>90%) but suffers from a moderate specificity (50 to 80% according to the type of cancer). In parallel, although it is strongly subjective, the act of palpation remains today a major act in the workflow of breast screening. Since Egyptian ancient ages, the physicians practise the act of palpating body parts in order to determine tissues stiffness and a hardly deformed mass within an organ is often related to the presence of an abnormal lesion. Palpation is not only useful for screening and diagnosis as the surgeon also uses it during interventions to be effectively guided towards the pathological area. Recently, new techniques based on ultrasound or magnetic resonance imaging finally made it possible to map organs elasticity in a quantitative way. These "elastography" techniques could play soon an important role in medical imaging. © 2007 Elsevier Masson SAS. All rights reserved. Mots-clés: Breast; Cancer; Diagnostic; Elastography; Magnetic resonance imaging; Screening; Ultrasound; contrast medium; breast cancer; cancer diagnosis; echography; Egypt; elastography; histology; human; imaging; mammography; morbidity; nuclear magnetic resonance imaging; palpation; physician; screening; sensitivity and specificity; short survey; surgeon; ultrasound
Compensating for bone interfaces and respiratory motion in high-intensity focused ultrasound Tanter, M., M. Pernot, J.-F. Aubry, G. Montaldo, F. Marquet, and M. Fink International Journal of Hyperthermia 23, no. 2, 141-151 (2007) Résumé: Bursts of focused ultrasound energy a thousand times more intense than diagnostic ultrasound have become a non-invasive option for treating cancer, from breast to prostate or uterine fibroid, during the last decade. Despite this progress, many issues still need to be addressed. First, the distortions caused by defocusing obstacles, such as the skull or ribs, on the ultrasonic therapeutic beam are still being investigated. Multi-element transducer technology must be used in order to achieve such transcranial or transcostal adaptive focusing. Second, the problem of motion artifacts, a key component in the treatment of abdominal lesions, has been shown significantly to influence the efficacy and treatment time. Though many methods have been proposed for the detection of organ motion, little work has been done to develop a comprehensive solution including motion tracking and feedback correction in real time. This paper is a review of the work achieved by authors in transcranial high-intensity focused ultrasound (HIFU), transcostal HIFU and motion compensated HIFU. For these three issues, the optimal solution can be reached using the same technology of multi-element transducers devices able to work both in transmit and receive modes. Mots-clés: Adaptive focusing; Brain therapy; Elastography; Monitoring; Motion correction; Time reversal; abdominal disease; animal experiment; animal model; article; artifact; brain tumor; clinical effectiveness; controlled study; diagnostic imaging; feedback system; high intensity focused ultrasound; motion; non invasive procedure; nonhuman; skull; thorax; ultrasound transducer; Animals; Artifacts; Bone and Bones; Brain Neoplasms; Feedback; Humans; Liver Diseases; Motion; Respiration; Ribs; Transducers; U
Focusing beyond the diffraction limit with far-field time reversal Lerosey, G., J. De Rosny, A. Tourin, and M. Fink Science 315, no. 5815, 1120-1122 (2007) Résumé: We present an approach for subwavelength focusing of microwaves using both a time-reversal mirror placed in the far field and a random distribution of scatterers placed in the near field of the focusing point. The far-field time-reversal mirror is used to build the time-reversed wave field, which interacts with the random medium to regenerate not only the propagating waves but also the evanescent waves required to refocus below the diffraction limit. Focal spots as small as one-thirtieth of a wavelength are described. We present one example of an application to telecommunications, which shows enhancement of the information transmission rate by a factor of 3. Mots-clés: diffraction; microwave radiation; telecommunication; wavelength; acoustics; article; diffraction; lens; lithotripsy; microwave radiation; priority journal; scanning near field optical microscopy; sound transmission; technology; telecommunication; time; ultrasound
Acoustic source localization model using in-skull reverberation and time reversal Catheline, S., M. Fink, N. Quieffin, and R. K. Ing Applied Physics Letters 90, no. 6 (2007) Résumé: A processing model of localization based on time reversal of the reverberated sound in a human skull is proposed. The underlying general idea is that bones act as antenna, gathering and conducting information about spatial positioning. Decoding this information is achieved with a time reversal analysis. Tested in a model experiment, the localization works in the azimuthal and sagittal plans, for single or multiple sound sources. Its efficiency is also demonstrated for one sided hearing people. The authors anticipate that this general antennalike concept can be applied to many animals that use sound localization as well as to future design for microphone devices or sonars. © 2007 American Institute of Physics. Mots-clés: Acoustic signal processing; Antennas; Bone; Microphones; Sonar; Acoustic source localization models; Sagittal plans; Spatial positioning; Time reversal analysis; Reverberation
Acoustic impact localization in plates: Properties and stability to temperature variation Ribay, G., S. Catheline, D. Clorennec, R. K. Ing, N. Quieffin, and M. Fink IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 54, no. 2, 378-384 (2007) Résumé: Localizing an impact generated by a simple finger knock on plate-shaped solid objects is made possible in an acoustic time reversal experiment. It is shown that the technique works with a single accelerometer. To better understand the phenomenon and to know exactly the nature of the created waves, a two-dimensional (2-D) elastic simulation is used, showing that in a very good approximation the Ao Lamb mode is the only propagating one. However, it is shown that, within one wavelength distance from the edges, evanescent waves must be taken into account. As a first consequence, the ability to distinguish two neighboring impacts improves when the plate thickness decreases and the frequency increases. As a second consequence, it is expected theoretically that temperature variations lead to a stretching or a contraction of acoustic signatures. The experimental demonstration used a heterodyne interferometer to measure the impulse responses created by a knock on a plate during the cooling. A simple algorithm is shown to perfectly compensate for temperature impacts, which demonstrates the feasibility of the technique for outdoor time reversal interactive experiments. © 2007 IEEE. Mots-clés: Accelerometers; Algorithms; Approximation theory; Computer simulation; Plates (structural components); Acoustic impact localization; Acoustic signatures; Temperature variations; Acoustic distortion; acoustics; article; computer simulation; methodology; radiation dose; radiation scattering; sensitivity and specificity; stimulation; temperature; theoretical model; transducer; vibration; Acoustics; Computer Simulation; Models, Theoretical; Physical Stimulation; Radiation Dosage; Scattering, Radiati
Non-invasive transcranial ultrasound therapy guided by CT-scans Marquet, F., M. Pernot, J. F. Aubry, G. Montaldo, M. Tanter, and M. Fink Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 1, 683-687 (2006) Résumé: Brain therapy using focused ultrasound remains very limited due to the strong aberrations induced by the skull. A technique using time-reversal was validated recently in-vivo on 20 sheep. The principal handicap of this technique is the need of an hydrophone at the focal point for the first step of the time-reversal procedure, which is minimally invasive but lightly traumatizing. A completely noninvasive therapy requires a reliable model of the acoustical properties of the skull in order to simulate this first step. 3-D simulations based on high-resolution CT images of a skull have been successfully performed with a finite differences code developed in our Laboratory. Thanks to the skull porosity, directly extracted from the CT images, we reconstructed acoustic speed, density and absorption maps and performed the computation. Computed wavefronts are in good agreement with experimental wavefronts acquired through the same part of the skull and this technic was validated in-vitro in the laboratory. A stereotactic frame has been designed and built in order to perform non invasive transcranial focusing. Here we will describe all the steps of our new protocol, from the CT-scans to the therapy treatment and the first in vivo results on monkeys will be presented. This protocol is based on protocols already existing in radiotherapy. Mots-clés: animal; article; brain; computer assisted diagnosis; computer assisted therapy; computer assisted tomography; equipment; equipment design; evaluation; Haplorhini; instrumentation; methodology; pilot study; radiography; stereotactic procedure; ultrasound therapy; Animals; Brain; Equipment Design; Equipment Failure Analysis; Haplorhini; Pilot Projects; Radiographic Image Interpretation, Computer-Assisted; Stereotaxic Techniques; Therapy, Computer-Assisted; Tomography, X-Ray Computed; Ultrasonic Th
In Vivo Achilles Tendon Elasticity Assessment using Supersonic Shear Imaging: a feasibility study Brum, J., M. Bernal, M. Fink, J. L. Gennisson, and M. Tanter IEEE International Ultrasonics Symposium, 1162-1165 (2013) Mots-clés: Achilles tendon; transverse isotropy; Lamb waves; viscoelasticity; supersonic shear imaging; shear wave spectroscopy
Cross Validation of Supersonic Shear Wave Imaging (SSI) with Classical Rheometry during Blood Coagulation over a very large Bandwidth Miguel, B., J.-L. Gennisson, M. Fink, M. Tanter, and P. Flaud IEEE International Ultrasonics Symposium, 1773-1776 (2013) Mots-clés: Deep venous thrombosis; Blood coagulation; rheometry; shear wave elastography
Non-invasive transcranial ultrasound therapy guided by CT-scans Marquet, F., M. Pernot, J.-F. Aubry, G. Montaldo, M. Tanter, and M. Fink Annual International Conference of the IEEE Engineering in Medicine and Biology - Proceedings, 683-687 (2006) Résumé: Brain therapy using focused ultrasound remains very limited due to the strong aberrations induced by the skull. A technique using time-reversal was validated recently in-vivo on 20 sheeps [1]. The principal handicap of this technique is the need of an hydrophone at the focal point for the first step of the time-reversal procedure, which is minimally invasive but lightly traumatizing. A completely noninvasive therapy requires a reliable model of the acoustical properties of the skull in order to simulate this first step. 3-D simulations based on high-resolution CT images of a skull have been successfully performed with a finite differences code developed in our Laboratory. Thanks to the skull porosity, directly extracted from the CT images, we reconstructed acoustic speed, density and absorption maps and performed the computation. Computed wavefronts are in good agreement with experimental wavefronts acquired through the same part of the skull and this technic was validated in-vitro in the laboratory[2]. A stereotactic frame has been designed and built in order to perform non invasive transcranial focusing. Here we will describe all the steps of our new protocol, from the CT-scans to the therapy treatment and the first in vivo results on monkeys will be presented. This protocol is based on protocols already existing in radiotherapy [3]. © 2006 IEEE. Mots-clés: Aberrations; Computerized tomography; Hydrophones; Noninvasive medical procedures; Radiotherapy; Finite differences code; Skull; Transcranial focusing; Ultrasonic applications
In-vivo non-invasive motion tracking and correction in High Intensity Focused Ultrasound therapy Marquet, F., M. Pernot, J.-F. Aubry, M. Tanter, G. Montaldo, and M. Fink Annual International Conference of the IEEE Engineering in Medicine and Biology - Proceedings, 688-691 (2006) Résumé: A method for tracking locally the 3D motion of biological tissues is developed and applied to the correction of motion during High Intensity Focused Ultrasound (HIFU) therapy. The motion estimation technique is based on an accurate ultrasonic speckle tracking method. A pulse-echo sequence is performed for a subset of the transducers of a phased array. For each of these sub-apertures, the displacement is estimated by computing the 1D cross-correlation of the backscattered signals acquired at two consecutive times. The local 3D motion vector is then computed using a inversion algorithm. This technique is experimentally validated in vivo on anesthetized pigs. The 3D motion of liver tissues is tracked in real-time. The technique is combined with HIFU sequences and a real-time feedback correction of the HIFU beam is achieved by adjusting the delays of each channel. The sonications "locked on target" are interleaved with very motion estimation sequences. © 2006 IEEE. Mots-clés: Algorithms; Motion estimation; Speckle; Tissue; Transducers; High Intensity Focused Ultrasound (HIFU); Motion vectors; Real-time feedback correction; Ultrasonic applications
Time-reversal of photo-acoustic waves generated by optical contrasts in an optically diffusive tissue phantom Bossy, E., K. Daoudi, A.-C. Boccara, M. Tanter, and M. Fink Proceedings - IEEE Ultrasonics Symposium 1, 1635-1638 (2006) Résumé: Time-reversal of ultrasonic waves allows focusing ultrasound through complex media, such as highly aberrating or highly diffusive media. Time-reversal is based on the detection and re-emission of waves generated by ultrasound sources located within the investigated medium. Classically, these sources consist of high acoustic contrasts echoing ultrasonic waves generated by an incident ultrasonic field, or directly by point-like transducers inserted in the medium. In this work, we use contrast of optical nature as sources of photo-acoustic waves to perform time-reversal experiments. Briefly, photo-acoustic waves are ultrasonic waves generated by the thermoelastic expansion following the absorption of a light pulse. A tissue phantom with optical contrast was fabricated by embedding an optically absorbing gel sphere (with a diameter of approximately 1 mm and an optical absorption coefficient on the order of 0.5 mm -1) in an optically diffusive intralipid solution (reduced scattering coefficient on the order of 10 cm -1). A Q-switched pulsed Nd:YAG laser was used to illuminate the tissue phantom with 80 mJ nanosecond laser pulses. A 1.5 MHz ultrasound array connected to a 64-channel time-reversal electronics was used to detect, record and time-reverse the photo-acoustic signals back towards the absorbing gel sphere. The quality of the focusing was assessed in the presence of a strong acoustically aberrating medium, and was found to be identical to that obtained without aberrator. As an example of application, B-mode images of several nylon wires were built in the presence of the aberrator, based on the time-reversed and steered wavefront generated by an absorbing gel sphere hung to one of the wire. © 2006 IEEE. Mots-clés: Photo-acoustic generation; Time-reversal; Ultrasound focusing; Acoustic generation; Acoustic signals; B-mode images; Complex media; Diffusive media; Gel spheres; Intralipids; Light pulse; Nanosecond laser pulse; Optical absorption coefficients; Optical contrast; Pulsed Nd:YAG laser; Q-switched; Re-emission; Reduced scattering coefficients; Thermoelastic expansion; Time-reversal; Time-reversed; Tissue phantom; Ultrasonic field; Ultrasound arrays; Ultrasound focusing; Ultrasound sources; Absorptio
In-vivo non-invasive motion tracking and correction in high intensity focused ultrasound therapy Marquet, F., M. Pernot, J. F. Aubry, M. Tanter, G. Montaldo, and M. Fink Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 1, 688-691 (2006) Résumé: A method for tracking locally the 3D motion of biological tissues is developed and applied to the correction of motion during high intensity focused ultrasound (HIFU) therapy. The motion estimation technique is based on an accurate ultrasonic speckle tracking method. A pulse-echo sequence is performed for a subset of the transducers of a phased array. For each of these sub-apertures, the displacement is estimated by computing the 1D cross-correlation of the backscattered signals acquired at two consecutive times. The local 3D motion vector is then computed using a inversion algorithm. This technique is experimentally validated in vivo on anesthetized pigs. The 3D motion of liver tissues is tracked in real-time. The technique is combined with HIFU sequences and a real-time feedback correction of the HIFU beam is achieved by adjusting the delays of each channel. The sonications "locked on target" are interleaved with very motion estimation sequences. Mots-clés: animal; article; artifact; computer assisted diagnosis; computer assisted therapy; echography; liver; methodology; motion; reproducibility; sensitivity and specificity; swine; ultrasound therapy; Animals; Artifacts; Image Interpretation, Computer-Assisted; Liver; Motion; Reproducibility of Results; Sensitivity and Specificity; Swine; Therapy, Computer-Assisted; Ultrasonic Therapy; Ultrasonography
Ultrafast ultrasonic imaging of in vivo muscle contraction Deffieux, T., J.-L. Gennisson, M. Tanter, and M. Fink Proceedings - IEEE Ultrasonics Symposium 1, 1001-1004 (2006) Résumé: Although numerous techniques are commonly used to study muscular or neuromuscular diseases, in vivo muscle contraction remains a difficult event to image in real time. On one hand, time accurate techniques such as for example, mechanomyography, electromyography, or acceleromyography; allow only the assessment of global parameters of musculo-tendinous complex. These estimated parameters are classically the force developed by a group of muscles fibers during contraction, the compound action potential or the acceleration of a muscle. On the other hand, mapping of local muscle structure parameters during contraction with a sub-millimetric resolution can be achieved by magnetic resonance imaging or ultrasound Doppler tissue imaging. However, these imaging modalities are not fast enough (less than hundreds of frames per second) to follow transient phenomena. Here, a new way of imaging the motion of an in vivo contracting muscle is proposed. The principle is to use an ultrafast ultrasound scanner to follow with a sub-millimetric resolution the axial motion of the muscle tissue in a two dimensional (2D) plane. This imaging technique designed at the "Laboratoire Ondes et Acoustique" for transient elastography, gives 2D radio frequency images at a few thousands Hertz (up to 5000 frames.s -1) and leads to both local and transient displacements of the muscle in vivo. Displacements as low as one micrometer are computed from the one dimensional (1D) cross-correlation between consecutive images. From these displacements, both local and transient informations on the muscle contraction are extracted such as the contraction time, the relaxation time or the mean velocity of the propagation of the contraction along a muscle fiber. During experiments the ultrafast scanner driving a 128 elements 8 MHz probe triggers a homemade electrostimulation device linked to a pair of electrodes placed on the motor point of the biceps brachii and at the elbow junction. In vivo studies of the contraction of a muscle are reported here by these first transient experiments achieved on the biceps brachii. The velocity distribution of the displacements induced in the tissue during contraction is measured as well as the main temporal features of the contraction. © 2006 IEEE. Mots-clés: Electrical and mechanical activities of the muscle; In vivo muscle contraction; Ultrafast ultrasonic imaging; Axial motions; Biceps brachii; Commonly used; Compound action potentials; Consecutive images; Cross correlations; Doppler tissue imaging; Electrical and mechanical activities of the muscle; Electrostimulation; Estimated parameter; Frames per seconds; Global parameters; Imaging modality; In-vivo; Mean velocities; Mechanomyography; Muscle contractions; Muscle fiber; Muscle structures; Musc
A 3D Elastography System based on the Concept of Ultrasound-Computed Tomography for In Vivo Breast Examination Gennisson, J.-L., T. Deffieux, R. Sinkus, P. Annic, M. Pernot, F. Cudeiro, G. Montaldo, M. Tanter, M. Fink, and J. Bercoff Proceedings - IEEE Ultrasonics Symposium 1, 1037-1040 (2006) Résumé: Elastography holds great promises for the additional characterization of lesions especially in the domain of breast cancer diagnosis. Most ultrasound based approaches have so far been limited to a one dimensional (1D) or at most two dimensional (2D) displacement estimation in one plane. This leads for the general case to sparse data which cannot be used to solve the full three dimensional (3D) wave equation in an unbiased manner. For instance contributions from the compressional wave cannot be removed via application of the curl operator. In order to overcome this limitation we developed an ultrasound based elastography system which uses the concept of computed tomography for data acquisition in combination with 2D vector displacement estimation within the plane of the ultrasound beam. The vector displacement estimation is achieved using the concept of adaptive subapertures during the receive beamforming process. The object of interest is scanned using a conventional ultrasonic probe (4 MHz, 128 elements) from different directions on a circular orbit. The transducer is translated perpendicular to the orbit (~10 times) for each angle which leads to several block datasets (~30 blocks) each containing 2D displacement information. Thereby, the displacement of each voxel within the object is measured several times from different directions. This provides high resolution volumic 3D displacement fields after regridding each dataset from polar to Cartesian coordinates. The data acquisition system is contained within a water tank underneath a standard breast biopsy table. This enables in vivo measurements with the patient in prone position. Thereby, the 3D acquisition as already developed in the area of Magnetic Resonance Elastography (MRE), is brought to the ultrasonic field. Initial phantom experiments were conducted with steady state mechanical excitation at 150 Hz. Inclusions are clearly visible in the complex shear modulus as reconstructed from inverting the full 3D wave equation. Taking benefit of the ultrafast acquisition speed of our ultrasound system, the proposed method allows to measure volumic datasets within clinically acceptable time. The method provides for each voxel of the 3D volume the frequency dependence of the complex shear modulus which in turn is linked to the underlying rheology of the material. This represents the proof of concept for a spectroscopic approach of elastography suitable for clinical application. The system enables the study of rheological properties of tumors which should further extend the diagnostic gain of elastography. © 2006 IEEE. Mots-clés: 3D elastography; Full inverse problem; Ultrafast imaging; 2-D displacement; 3-D displacement; 3D acquisition; 3D elastography; 3D wave equation; Breast biopsies; Breast cancer diagnosis; Cartesian coordinate; Circular orbit; Clinical application; Complex shear modulus; Compressional waves; Computed Tomography; Data acquisition system; Data sets; Displacement estimation; Elastography; Frequency dependence; Full inverse problem; High resolution; In-vivo; In-vivo measurement; Magnetic resonance ela
Time reversal of photoacoustic waves Bossy, E., K. Daoudi, A.-C. Boccara, M. Tanter, J.-F. Aubry, G. Montaldo, and M. Fink Applied Physics Letters 89, no. 18, 184108 (2006) Résumé: In this work, the authors use the photoacoustic effect to create a source for ultrasonic time-reversal experiments. Photoacoustic waves were generated by an optically absorbing gel sphere excited by a laser pulse in a highly optically diffusive solution and recorded with an ultrasound array controlled by a time-reversal electronics. The emission of the time-reversed photoacoustic waves allowed the refocusing of the ultrasound towards the optical absorber, in particular, in the presence of a strongly acoustically defocusing medium. The authors illustrate how the technique can be applied to perform acoustical imaging in the presence of a strong acoustical aberration. © 2006 American Institute of Physics. Mots-clés: Aberrations; Gels; Imaging techniques; Optical properties; Photoacoustic effect; Ultrasonics; Absorbing gel; Acoustical aberration; Photoacoustic waves; Acoustic waves
Ultrafast imaging of in vivo muscle contraction using ultrasound Deffieux, T., J.-L. Gennisson, M. Tanter, M. Fink, and A. Nordez Applied Physics Letters 89, no. 18 (2006) Résumé: In this letter, an innovative way of imaging transient and local shear vibrations of an in vivo contracting muscle is proposed. The principle is to use an ultrafast ultrasound scanner (up to 5000 frames s-1) able to follow with a submillimeter resolution the motion of the muscle tissue in a two dimensional plane. This ultrafast echographic imaging technique leads to both local and transient in vivo studies of the contraction of a muscle as reported by these first experiments done on the biceps brachii. © 2006 American Institute of Physics. Mots-clés: Imaging techniques; Medical imaging; Tissue; Ultrafast phenomena; Ultrasonics; Echographic imaging technique; Shear vibrations; Ultrasound scanner; Muscle
Nonlinear viscoelastic properties of tissue assessed by ultrasound Sinkus, R., J. Bercoff, M. Tanter, J.-L. Gennisson, C. El Khoury, V. Servois, A. Tardivon, and M. Fink IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 53, no. 11, 2009-2018 (2006) Résumé: A technique to assess qualitatively the presence of higher-order viscoelastic parameters is presented. Low-frequency, monochromatic elastic waves are emitted into the material via an external vibrator. The resulting steady-state motion is detected in real time via an ultra fast ultrasound system using classical, one-dimensional (1-D) ultrasound speckle correlation for motion estimation. Total data acquisition lasts only for about 250 ms. The spectrum of the temporal displacement data at each image point is used for analysis. The presence of nonlinear effects is detected by inspection of the ratio of the second harmonics amplitude with respect to the total amplitude summed up to the second harmonic. Results from a polyacrylamide-based phantom indicate a linear response (i.e., the absence of higher harmonics) for this type of material at 65 Hz mechanical vibration frequency and about 100 μm amplitude. A lesion, artificially created by injection of glutaraldehyde into a beef specimen, shows the development of higher harmonics at the location of injection as a function of time. The presence of upper harmonics is clearly evident at the location of a malignant lesion within a mastectomy. © 2006 IEEE. Mots-clés: Elastic waves; Nonlinear systems; Real time systems; Speckle; Ultrasonic applications; Vibrators; Viscoelasticity; External vibrators; Polyacrylamide based phantom; Steady state motion; Viscoelastic parameters; Tissue; algorithm; animal; article; biological model; breast tumor; computer assisted diagnosis; computer simulation; echography; elasticity; human; image enhancement; image quality; methodology; nonlinear system; pathophysiology; reproducibility; sensitivity and specificity; viscosity; A
Adaptive focusing for transcranial ultrasound imaging using dual arrays Vignon, F., J. F. Aubry, M. Tanter, A. Margoum, and M. Fink Journal of the Acoustical Society of America 120, no. 5, 2737-2745 (2006) Résumé: Ultrasonic brain imaging remains difficult and limited because of the strong aberrating effects of the skull (absorption, diffusion and refraction of ultrasounds): high resolution transcranial imaging would require adaptive focusing techniques in order to correct the defocusing effect of the skull. In this paper, a noninvasive brain imaging device is presented. It is made of two identical linear arrays of 128 transducers located on each side of the skull. It is possible to separate the respective influence of the two bone windows on the path of an ultrasonic wave propagating from one array to the other, and thus estimate at each frequency the attenuation and phase shift locally induced by each bone window. The information obtained on attenuation and phase is used to correct the wave fronts that have to be sent through the skull in order to obtain a good focusing inside the skull. Compared to uncorrected wave fronts, the spatial shift of the focal spot is corrected, the width of the focal spot is reduced, and the sidelobes level is decreased up to 17 dB. Transcranial images of a phantom are presented and exhibit the improvement in image quality provided by this new noninvasive adaptive focusing method. © 2006 Acoustical Society of America. Mots-clés: Brain; Image quality; Light absorption; Phase shifters; Refraction; Transducers; Ultrasonics; Adaptive focusing; Linear arrays; Ultrasonic brain imaging; Ultrasonic wave propagation; Medical imaging; article; device; Doppler echography; Fourier analysis; imaging; mathematical computing; model; phantom; priority journal; skull; technique; transducer; ultrasound; Adult; Child; Echoencephalography; Fourier Analysis; Humans; Image Enhancement; Phantoms, Imaging; Skull; Transducers
Gaussian beams and Legendre polynomials as invariants of the time reversal operator for a large rigid cylinder Aubry, A., J. De Rosny, J.-G. Minonzio, C. Prada, and M. Fink Journal of the Acoustical Society of America 120, no. 5, 2746-2754 (2006) Résumé: The DORT method (French acronym for decomposition of the time reversal operator) is an active remote sensing technique using an array of antennas for the detection and localization of scatterers. This method is based on the singular value decomposition of the interelement response matrix. In this paper an analytical expression of the singular vectors due to the reflection from a large rigid cylinder is provided. Depending on the array aperture, two asymptotic regimes are described. It is shown that the singular vectors correspond to Hermite-Gaussian modes for large apertures and Legendre polynomials for small ones. Using perturbation theory, the corresponding singular values are deduced. Theoretical predictions are in good agreement with experimental results. © 2006 Acoustical Society of America. Mots-clés: Acoustic fields; Antenna arrays; Polynomials; Remote sensing; Vectors; DORT method; Gaussian modes; Rigid cylinder; Singular value decomposition; Gaussian noise (electronic); acoustics; article; decomposition; mathematical analysis; mathematical computing; model; normal distribution; priority journal; remote sensing; technique; transducer
Time-reversal imaging of seismic sources and application to the great Sumatra earthquake Larmat, C., J.-P. Montagner, M. Fink, Y. Capdeville, A. Tourin, and E. Clévédé Geophysical Research Letters 33, no. 19 (2006) Résumé: The increasing power of computers and numerical methods (like spectral element methods) allows continuously improving modelization of the propagation of seismic waves in heterogeneous media and the development of new applications in particular time reversal in the three-dimensional Earth. The concept of time-reversal (hereafter referred to as TR) was previously successfully applied for acoustic waves in many fields like medical imaging, underwater acoustics and non destructive testing. We present here the first application at the global scale of TR with associated reverse movies of seismic waves propagation by sending back long period time-reversed seismograms. We show that seismic wave energy is refocused at the right location and the right time of the earthquake. When TR is applied to the Sumatra-Andaman earthquake (26 Dec. 2004), the migration of the rupture from the south towards the north is retrieved. Therefore, TR is potentially interesting for constraining the spatio-temporal history of complex earthquakes. Copyright 2006 by the American Geophysical Union. Mots-clés: Acoustic waves; Earth (planet); Earthquakes; Nondestructive examination; Seismic waves; Underwater acoustics; Reverse movies; Sumatra earthquake; Time-reversal imaging; Seismic prospecting; acoustic wave; earthquake rupture; heterogeneous medium; imaging method; numerical model; seismic source; seismic wave; seismogram; Sumatra earthquake 2004; wave energy; wave propagation
Time reversal telecommunications in complex environments Tourin, A., G. Lerosey, J. De Rosny, A. Derode, and M. Fink Comptes Rendus Physique 7, no. 7, 816-822 (2006) Résumé: The time reversal technique is well known in acoustics and has lead to remarkable applications in ultrasound and underwater acoustics. Here we propose to apply it to MIMO (Multiple Input - Multiple Output) UWB (Ultra Wide Band) communication: in a first 'training' step, the intended user transmits an electromagnetic pulse that propagates in a medium, where it undergoes multiple reflections. The resulting signals are recorded at the base station by one or more antennas, time reversed and used to precode the transmitted symbols. The resulting sequences are sent back by the antennas. The time-reversed wave retraces its former paths and leads to a focus of the message in space and time at the receiver. The equalization step is thus simplified since TR compensates for the reverberation caused by the channel. Furthermore, TR takes advantage of the multipaths to increase the signal strength at the receiver and to improve spatial focusing. To cite this article: A. Tourin et al., C. R. Physique 7 (2006). © 2006 Académie des sciences. Mots-clés: MIMO; Multiple scattering; Reverberation; Time reversal; UWB
Multiple scattering between two elastic cylinders and invariants of the time-reversal operator: Theory and experiment Minonzio, J.-G., C. Prada, A. Aubry, and M. Fink Journal of the Acoustical Society of America 120, no. 2, 875-883 (2006) Résumé: The decomposition-of-the-time-reversal-operator method is an ultrasonic method based on the analysis of the array response matrix used for detection and characterization. The eigenvalues and the eigenvectors of the time-reversal operator (equivalent to the singular values and the singular vectors of the array response matrix) provide information on the localization and nature of scatterers in the insonified medium. Here, the eigenmodes of the time-reversal operator are studied for two elastic cylinders: The effects of multiple scattering and anisotropic scattering are considered. Analytical expressions for the singular values are established within the isotropic scattering approximation. Then, the comparison with a complete model is presented, putting in evidence the importance of the anisotropy of the scattering. Experiments, carried out at central frequency 1.5 MHz on 0.25 mm diameter nylon and copper cylinders embedded in water, confirm the theory. In particular, the small cylinder limit and the effect of the dominant quadrupolar normal mode of nylon are discussed. © 2006 Acoustical Society of America. Mots-clés: Anisotropy; Approximation theory; Cylinders (shapes); Eigenvalues and eigenfunctions; Mathematical operators; Vectors; Elastic cylinders; Insonified medium; Isotropic scattering approximation; Quadrupolar normal mode; Acoustic wave scattering; acoustics; analytic method; anisotropy; article; decomposition; electromagnetic radiation; imaging system; model; priority journal; sound transmission; stimulus response; theory; ultrasound
Time-reversal acoustics in complex environments Fink, M. Geophysics 71, no. 4, SI151-SI164 (2006) Résumé: Time-reversal mirrors (TRMs) refocus an incident acoustic field to the position of the original source regardless of the complexity of the propagation medium. TRMs have now been implemented in a variety of physical scenarios from megahertz ultrasonics with aperture sizes of the order of centimeters to ocean acoustics at hundreds to thousands of hertz with aperture sizes of the order of hundreds of meters. Common to this broad range of scales is a remarkable robustness - exemplified by observations at all scales - that the more complex the medium between the probe source and the TRM, the sharper the focus. The relationship between the medium complexity and the size of the focal spot is studied in this paper. This relationship is certainly the most exciting property of TRM compared to standard focusing devices. A TRM acts as an antenna that uses complex environments to appear wider than it is, resulting in a broadband pulse with a refocusing quality that does not depend on the TRM aperture. In this paper, we investigate both the role of the time-reversal window duration and the bandwidth of the time-reversed signals for various media (waveguide, closed cavity, random medium). © 2006 Society of Exploration Geophysicists. Mots-clés: Acoustic imaging; Seismic waves; Seismology; Seismometers; Acoustic fields; Acoustic imaging; Bandwidth; Mirrors; Seismic waves; Seismographs; Wave propagation; Waveguides; Time-reversal mirrors (TRMs); Seismology; acoustic imagery; acoustics; seismic wave; seismograph; seismology; ultrasonics
Time reversal operator decomposition with focused transmission and robustness to speckle noise: Application to microcalcification detection Robert, J.-L., M. Burcher, C. Cohen-Bacrie, and M. Fink Journal of the Acoustical Society of America 119, no. 6, 3848-3859 (2006) Résumé: The decomposition of the time reversal operator (DORT) is a detection and focusing technique using an array of transmit-receive transducers. In the absence of noise and under certain conditions, the eigenvectors of the time reversal operator contain the focal laws to focus ideally on well-resolved scatterers even in the presence of strong aberration. This paper describes a new algorithm, FDORT, which uses focused transmission schemes to acquire the operator. It can be performed from medical scanner data. A mathematical derivation of this algorithm is given and it is compared with the conventional algorithm, both theoretically and with numerical experiments. In the presence of strong speckle signals, the DORT method usually fails. The influence of the speckle noise is explained and a solution based on FDORT is presented, that enables detection of targets in complex media. Finally, an algorithm for microcalcification detection is proposed. In-vivo results show the potential of these techniques. © 2006 Acoustical Society of America. Mots-clés: Aberrations; Algorithms; Eigenvalues and eigenfunctions; Mathematical operators; Robustness (control systems); Transducers; Decomposition of the time reversal operator (DORT); Mathematical derivation; Microcalcification detection; Acoustic variables control; algorithm; article; comparative study; decomposition; experiment; mathematical computing; mathematical model; mathematical parameters; noise; priority journal; signal detection; theoretical study; ultrasound; ultrasound scanner
"ultrasonic stars" for time reversal focusing using induced cavitation bubbles Pernot, M., G. Montaldo, M. Tanter, and M. Fink AIP Conference Proceedings 829, 223-227 (2006) Résumé: Time reversal focusing with ultrasonic arrays is a way to focus waves through heterogeneous media. It requires a reference signal either sent by a small active source embedded in the medium or backscattered by a strong scatterer acting as a passive source. The potential of this method in ultrasonic medical imaging was already envisioned for aberration corrections. However, in many practical situations it is not possible to insert an active source in the medium or to rely on the presence of a unique strong scaterrer at focus in order to generate the reference signal. In analogy with the field of adaptive optics in astronomy, we propose here to create artificial "ultrasonic stars" in the body. The trick consists in creating cavitation bubbles inside the medium using one part of the ultrasonic probe. The bubble cavitation generates a spherical wave that propagates through medium heterogeneities to a time reversal array and is used as a reference signal for the time reversal method. This novel method is here experimentally validated for aberrations corrections in tissue mimicking phantoms. © 2006 American Institute of Physics. Mots-clés: Adaptive focusing; Bubble; Cavitation; HiFU; Time reversal; Ultrasound
Experimental investigation of time-reversal of photo-acoustic waves Bossy, E., G. Montaldo, M. Tanter, B. Forget, F. Ramaz, M. Fink, and C. Boccara Proceedings of SPIE - The International Society for Optical Engineering 6086 (2006) Résumé: Ultrasound focusing through complex media can be achieved using time-reversal techniques. These techniques make use of back-propagating ultrasonic waves generated by localized sources. Such sources generally consist of high acoustic contrasts echoing ultrasonic waves generated by an incident ultrasonic field, or directly by point-like transducers inserted at the desired focusing location. In this work, we experimentally investigate time-reversal of acoustic waves generated by photo-acoustic emission. A frequency-doubled Q-switched Nd:YAG laser was used to illuminate phantom with 5-ns laser pulses. A 128-element ultrasonic transducer array, with a center frequency of 1.5 MHz, was used to detect acoustic waves generated by optically absorbing targets suspended in water. A dedicated 32-channel electronics was used to time-reverse and re-emit the detected ultrasonic field. Gel spheres dyed with India ink (diameter approximately 1-2 mm) illuminated by the laser beam were used to generate the photo-acoustic waves. Time-reversal of the detected field was performed to focus ultrasound in the presence of highly defocusing media in front of the transducer array. We demonstrate how this allows correcting for the aberration in order to provide good quality images in the isoplanetic region surrounding the photo-acoustic source. Mots-clés: Optoacoustic emission; Photo-acoustic emission; Time-reversal; Ultrasound focusing; Acoustic waves; Backpropagation; Light emission; Transducers; Ultrasonics; Wave effects; Optoacoustic emission; Photo-acoustic emission; Time-reversal; Ultrasound focusing; Photoacoustic effect
Time reversal of wideband microwaves Lerosey, G., J. De Rosny, A. Tourin, A. Derode, and M. Fink Applied Physics Letters 88, no. 15 (2006) Résumé: In this letter, time reversal is applied to wideband electromagnetic waves in a reverberant room. To that end a multiantenna time reversal mirror (TRM) has been built. A 150 MHz bandwidth pulse at a central frequency of 2.45 GHz is radiated by a monopolar antenna, spread in time due to reverberation, recorded at the TRM, time reversed, and retransmitted. The time-reversed wave converges back to its source and focus in both time and space. The time compression is studied versus the number of antennas in the TRM and its bandwidth. The focal spot is also measured thanks to an eight-channel receiving array. © 2006 American Institute of Physics. Mots-clés: Arrays; Bandwidth; Microwave antennas; Mirrors; Reverberation; Monopolar antenna; Receiving array; Time reversal mirror (TRM); Microwaves
Time reversal of ultrasound through a phononic crystal Tourin, A., F. Van Der Biest, and M. Fink Physical Review Letters 96, no. 10 (2006) Résumé: In this Letter, we experimentally investigate time reversal focusing through a phononic crystal consisting of a periodic square arrangement of steel rods in water. An acoustic pulse is transmitted through the medium, received at a transducer array, time reversed and backpropagated. Both spatial focusing and time compression are studied and compared with those obtained through an equivalent disordered medium. With the phononic crystal, we do not observe the "hyperfocusing effect" that is typical of time reversal through disordered samples. © 2006 The American Physical Society. Mots-clés: Phononic crystals; Steel rods; Transducer array; Backpropagation; Photons; Steel; Transducers; Crystalline materials
The Stokes relations linking time reversal and the inverse filter Vignon, F., J.-F. Aubry, A. Saez, M. Tanter, D. Cassereau, G. Montaldo, and M. Fink Journal of the Acoustical Society of America 119, no. 3, 1335-1346 (2006) Résumé: Our aim in this paper is to show how two adaptive focusing techniques, Time Reversal (TR) and the Spatio Temporal Inverse Filter (STIF), are related by the Stokes equations linking waves transmitted and reflected through a medium. For that purpose a model experiment has been investigated: a solid plate located between two arrays of transducers. When sending a wave from an array to the other through the plate, multiple transmitted waves are induced. TR and STIF are used to cancel these echoes. The echoes can be suppressed by TR, using the two arrays cavity surrounding the plate. They can also be cancelled by STIF, inverting the transmission operator between the arrays. The STIF achieves echoes cancellation by using only the transmitted fields through the plate, whereas TR also requires the reflected fields. The STIF's strategy is analyzed in light of the Stokes relations: thanks to the reflections in the medium, it is able to simulate a TR cavity with only one array. A mathematical analysis of the matrix expression of the Stokes relations then leads to two iterative ways to invert the transmission operator. Finally, this general technique is applied to a more complex medium: a human skull bone.. © 2006 Acoustical Society of America. Mots-clés: Acoustic arrays; Computer simulation; Equations of motion; Transducers; Wave transmission; Inverse filters; Spatio Temporal Inverse Filter (STIF); Time Reversal (TR); Transmission operators; Adaptive filtering; acoustics; article; human; human tissue; mathematical analysis; mathematical computing; mathematical model; priority journal; skull; sound; time; transducer
"Ultrasonic stars" for time-reversal focusing using induced cavitation bubbles Pernot, M., G. Montaldo, M. Tanter, and M. Fink Applied Physics Letters 88, no. 3, 1-3 (2006) Résumé: Ultrasound waves can be focused by multichannel arrays through heterogeneous media using a time-reversal focusing method. In this method, it is required that a reference signal be either sent by a small active source embedded in the medium or backscattered by a strong scatterer acting as a passive source. The potential of this method in ultrasonic medical imaging has been already envisioned for aberration corrections. However, in many practical situations it is not possible to insert an active source in the medium or to rely on the presence of a unique strong scatterer in order to generate the reference signal. Analogous to the field of adaptive optics in astronomy, we propose here to create artificial "ultrasonic stars" in the body. The trick consists of first creating a bubble inside the medium using a section of the ultrasonic array. Due to cavitation, the bubble generates a spherical wave that propagates through a heterogeneous medium to the ultrasound array. The time-reversal method is then applied to the ultrasonic wave received by the array. This technique is experimentally validated for aberrations corrections in tissue mimicking phantoms. © 2006 American Institute of Physics. Mots-clés: Aberrations; Adaptive optics; Imaging systems; Medical imaging; Scattering; Ultrasonics; Cavitation bubbles; Tissue mimicking phantoms; Ultrasonic medical imaging; Ultrasound waves; Bubbles (in fluids)
High resolution ultrasonic brain imaging: Adaptive focusing based on twin-arrays Vignon, F., J.-F. Aubry, M. Tanter, and M. Fink ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings V, V973-V976 (2005) Résumé: Transcranial imaging of the brain is currently limited by the defocusing effect of the skull bone (absorption, diffusion and refraction of ultrasounds. A brief review of the various techniques developed in the last decades to correct the aberrations induced by the skull bone is first presented. A noninvasive brain imaging device is presented that takes into account the defocusing effect of the skull. This device is made of two identical "twin" linear arrays located on each side of the head. It is shown how to differentiate the respective influence of the two bone windows on the path of an ultrasonic wave going from one array to the other, and how to estimate at each frequency the attenuation and phase shift locally induced by each of the bone windows. This information is then used to perform adaptive focusing through the skull Compared to uncorrected wave fronts, the spatial shift of the focal point is cancelled, the width of the focal spot is reduced, and sidelobes level is decreased up to 10dB. Simulated structural transcranial images of a brain model are presented to exhibit the improvement in image quality provided by this new noninvasive adaptive focusing method. © 2005 IEEE. Mots-clés: Bone; Brain; Image quality; Mathematical models; Phase shift; Ultrasonics; Defocusing effect; Linear arrays; Skull bone; Transcranial imaging; Medical imaging
Time reversal and phase conjugation with acoustic waves: Industrial and medical applications Fink, M. 2005 Conference on Lasers and Electro-Optics, CLEO 3, 2334-2335 (2005)
Decomposition of the Time-reversal Operator applied to quantitative characterization of small elastic cylinders Minonzio, J.-G., C. Prada, and M. Fink Proceedings - IEEE Ultrasonics Symposium 2, 1147-1150 (2005) Résumé: Recent experiments showed how the DORT method can be used for the characterization of elastic cylinders imbedded in water [Minonzio et al., J. Acoust. Soc. Am. 117 (2), pp 789-798, 2005]. Here, the small cylinder limit (k0a < 0.5) is considered. The singular values of the array response matrix are studied. It is show that the first singular value is proportional to k0(α+ β)a2 and the second one is proportional to k0βa2 where a is the radius, α is the compressibility contrast, β is the density contrast between the cylinder and the fluid. Thus, the linear frequency dependence of the two singular values provides two equations with three unknowns, α, β and a. If one of these three parameters is known (for example, α is about 1 for metals), the other two can be determined. Measurements carried out for materials of α ranging from 0.6 to 0.99 and β between 0.1 and 1.6 are presented. A good agreement between calculated and experimental singular values was observed. Generalized expressions of the two first singular values are also given for k0a < 10. © 2005 IEEE. Mots-clés: Acoustic scattering; Characterization; Component; DORT method; Time-reversal; Acoustic wave scattering; Matrix algebra; Parameter estimation; Ultrasonic measurement; Acoustic scattering; DORT method; Time-reversal; Ultrasonic devices
Application of the DORT method to the detection and characterization of two targets in a shallow water wave-guide Minonzio, J.-G., D. Clorennec, A. Aubry, T. Folégot, T. Pélican, C. Prada, J. De Rosny, and M. Fink Oceans 2005 - Europe 2, 1001-1006 (2005) Résumé: The decomposition of the time-reversal operator (DORT In French) is an active array detection technique. It requires the measurement of the array response matrix K(ω) and consists in the analysis of the eigenvalues and the eigenvectors of the time-reversal operator K*K which provides information on the presence and localization of scatterers in the medium. It was shown that the DORT method allows to separate and localize pointlike scatterers in a shallow water wave-guide [J. Acoust. Soc. Am. Mordant et al. (1998) and Folégot et al. (2003)]. Here, we extend the study to the detection and frequency characterization of two spherical targets. Small scale ultrasonic experiments are performed with a 3.9 MHz 24 elements transducer array and two spheres of 2 and 3 mm diameter in a 31 mm deep wave-guide. These scatterers correspond to 15 < ka < 25 leading to a non-isotropic scattered field. We have developed a theoretical model taking into account the wave-guide and the acoustic properties of the spheres and using the partial waves decomposition of the scattered field. We calculate the singular values of the array response matrix. This theoretical approach is in good agreement with the experimental results. This 1/325th scale ultrasonic experiment corresponds to a shallow water experiment with a 12 kHz Vertical Linear Array (VLA). © 2005 IEEE. Mots-clés: Eigenvalues and eigenfunctions; Mathematical models; Matrix algebra; Transducers; Ultrasonic applications; Frequency characterization; Partial waves decomposition; Pointlike scatterers; Waveguides
Dual-arrays brain imaging prototype: Experimental in Vitro results Vignon, F., J.-F. Aubry, M. Tanter, A. Margoum, M. Fink, and J. M. Lecoeur Proceedings - IEEE Ultrasonics Symposium 1, 504-507 (2005) Résumé: Transcranial imaging of the brain is currently limited by the defocusing effect of the skull bone (absorption, diffusion and refraction of ultrasound A noninvasive brain imaging device is presented that takes into account the defocusing effect of the skull. This device is made of two identical "twin" linear arrays located on each side of the head. It is shown how to differentiate the respective influence of the two bone windows on the path of an ultrasonic wave going from one array to the other, and how to estimate at each frequency the attenuation and phase shifts locally induced by each of the bone windows. This information is then used to perform non invasive adaptive focusing through the skull. Compared to non corrected wavefronts used in the beamforming process of commercial scanners, the spatial shift of the focal point is cancelled, the width of the focal spot is reduced, and the sidelobes level is decreased up to 15dB. The technique has been used to acquire in vitro images of tissue phantoms behind a skull wall, exhibiting the image quality enhancement with respect to images obtained with cylindrical focusing. Further refinement should lead to an improvement of the image contrast greater than 20 dB compared to conventionnal scanners. © 2005 IEEE. Mots-clés: Aberration corrections; Adaptive focusing; Beamforming; Brain; Component; Inverse filter; Aberrations; Brain; Diffusion; Phase shift; Ultrasonics; Aberration corrections; Adaptive focusing; Inverse filter; Imaging techniques
Tactile time reversal interactivity: Experiment and modelization Ribay, G., D. Clorennec, S. Catheline, M. Fink, R. K. Ing, and N. Quieffin Proceedings - IEEE Ultrasonics Symposium 4, 2104-2107 (2005) Résumé: Thanks to the Time Reversal theory, a technique of localization of an impact generated by a simple finger knock on plate-shaped solid objects has been developed. It is shown that the technique works with only one cheap accelerometer, and that adding sensors increases the contrast of the localization pattern but not the resolution. To better understand the phenomenon and to know exactly the nature of the created waves, a 2D elastic simulation is used, showing that in a very good approximation the A0 Lamb mode is the only propagating one. Moreover, at around 1 cm from the edges, even the non-propagating modes are negligible compared with the A0 mode. Furthermore, the stability of the technique to temperature changes is studied. Indeed, the TR theory predicts that the localization is effective only if the acoustic medium reciprocity has not been broken by any change in the medium including wave speed variation due to temperature change. To this end, a laser interferometer coupled to a low frequency demodulator measures the impulse responses created by a knock on a plate during the cooling. Given that there is only one propagating wave (A0), it is expected that temperature variations lead to a stretching of acoustic signatures that can be compensated for thanks to a simple contraction: this is observed experimentally. This shows the feasibility of the technique for outdoor Time Reversal interactive experiment. © 2005 IEEE. Mots-clés: A0 Lamb mode; Evanescent waves; Impact localization; Temperature variation; Time reversal; Approximation theory; Computer simulation; Wave propagation; Evanescent waves; Impact localization; Temperature variation; Time Reversal theory; Ultrasonic waves
In solid localization of finger impacts using acoustic time-reversal process Ing, R. K., N. Quieffin, S. Catheline, and M. Fink Applied Physics Letters 87, no. 20, 1-3 (2005) Résumé: Time reversal in acoustics is a very efficient solution to focus sound back to its source in a wide range of materials including reverberating media. It expresses the following properties: A wave still has the memory of its source location. The concept presented in this letter first consists in detecting the acoustic waves in solid objects generated by a slight finger knock. In a second step, the information related to the source location is extracted from a simulated time reversal experiment in the computer. Then, an action (turn on the light or a compact disk player, for example) is associated with each location. Thus, the whole system transforms solid objects into interactive interfaces. Compared to the existing acoustic techniques, it presents the great advantage of being simple and easily applicable to inhomogeneous objects whatever their shapes. The number of possible touch locations at the surface of objects is shown to be directly related to the mean wavelength of the detected acoustic wave. © 2005 American Institute of Physics. Mots-clés: Acoustics; Computer simulation; Object recognition; Surface treatment; Acoustic time-reversal processes; Solid localization; Source location; Acoustic waves
Time reversal of electromagnetic waves and telecommunication Lerosey, G., J. De Rosny, A. Tourin, A. Derode, G. Montaldo, and M. Fink Radio Science 40, no. 6 (2005) Résumé: [1] Time reversal (TR) communication in various configurations (single input, single output (SISO); multiple inputs, single output (MISO); or multiple inputs, multiple outputs (MIMO)) is studied. In particular, we report an experimental demonstration of time reversal focusing with electromagnetic waves in a SISO scheme. An antenna transmits a 1 μs electromagnetic pulse at a central frequency of 2.45 GHz in a high-Q cavity. Another antenna records the strongly reverberated signal. The time-reversed wave is built and transmitted back by the same antenna acting now as a time reversal mirror. The wave is found to converge to its initial source and is compressed in time. The quality of focusing is determined by the frequency bandwidth and the spectral correlations of the field within the cavity. A spatial focusing of the compressed pulse is also shown. This experiment is the first step for a communication scheme based on time reversal. It would be very interesting for ultrawideband communication in complex media since TR would permit compensation for delay spreading. MISO and MIMO TR communications are discussed on the basis of small-scale experiments with ultrasound. In particular, the binary error rate of the method is studied as a function of both data rate and external noise. A simple theoretical approach explains the results. Copyright 2005 by the American Geophysical Union. Mots-clés: Antennas; Bandwidth; Error analysis; Functions; Telecommunication systems; Binary error rate; Complex media; Ultrawideband communication; Electromagnetic waves
Building three-dimensional images using a time-reversal chaotic cavity Montaldo, G., D. Palacio, M. Tanter, and M. Fink IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 52, no. 9, 1489-1497 (2005) Résumé: The design of two-dimensional (2-D) arrays for three-dimensional (3-D) ultrasonic imaging is a major challenge in medical and nondestructive applications. Thousands of transducers are typically needed for focusing and steering in a 3-D volume. In this article, we propose a different concept allowing us to obtain electronic 3-D focusing with a small number of transducers. The basic idea is to couple a small number of transducers to a chaotic reverberating cavity with one face in contact with the body of the patient. The reverberations of the ultrasonic waves inside the cavity create at each reflection virtual transducers. The cavity acts as an ultrasonic kaleidoscope multiplying the small number of transducers and creating a much larger virtual transducer array. By exploiting time-reversal processing, it is possible to use collectively all the virtual transducers to focus a pulse everywhere in a 3-D volume. The reception process is based on a nonlinear pulse-inversion technique in order to ensure a good contrast. The feasibility of this concept for the building of 3-D images was demonstrated using a prototype relying only on 31 emission transducers and a single reception transducer. © 2005 IEEE. Mots-clés: Chaotic reverberating cavity; Non-linear pulse inversion; Three-dimensional imaging; Time-reversal chaotic cavity; Chaos theory; Nondestructive examination; Software prototyping; Three dimensional; Transducers; Ultrasonics; Ultrasonic imaging
Ultrafast Doppler reveals the mapping of cerebral vascular resistivity in neonates. Demene, C., M. Pernot, V. Biran, M. Alison, M. Fink, O. Baud, and M. Tanter Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism 34, no. 6, 1009-17 (2014)
Weak localization and time reversal of ultrasound in a rotational flow De Rosny, J., A. Tourin, A. Derode, P. Roux, and M. Fink Physical Review Letters 95, no. 7 (2005) Résumé: A one-channel time-reversal (TR) experiment is performed inside a rough reverberating cavity in the presence of a rotational flow. The amplitude of the TR wave is plotted versus the distance between the TR channel and the initial source: when they coincide, it exhibits a "time-reversal enhancement" (TRE). With no flow, the TRE is the same as the coherent backscattering enhancement (CBE). But contrary to CBE, the TRE peak is shown to be insensitive to the breaking down of reciprocity due to the flow. This new effect of weak localization is sustained by a diagrammatic approach. © 2005 The American Physical Society. Mots-clés: Coherent backscattering enhancement (CBE); Weak localization; Backscattering; Coherent light; Light sources; Rotational flow; Ultrasonics
Human muscle hardness assessment during incremental isometric contraction using transient elastography Gennisson, J. L., C. Cornu, S. Catheline, M. Fink, and P. Portero Journal of Biomechanics 38, no. 7, 1543-1550 (2005) Résumé: The aim of this study was to investigate the relationship between biceps brachii hardness using the transient elastography technique, and its activity level by quantifying the surface electromyographic signal (sEMG). Ten healthy subjects volunteered for this protocol. To assess the maximal biceps brachii myoelectric activity (sEMG-RMSm), subjects had to achieve their maximal voluntary contraction trial during an elbow flexion effort. They were then asked to perform an isometric biceps sEMG-RMS ramp trial in elbow flexion from 0% to 50% of their sEMG-RMSm in 120 s. A low-frequency pulse was sent every 5 s during all trials by an innovative shear elasticity probe previously placed over the belly of the biceps brachii allowing the calculation of a transverse shear modulus. The main results of this study were (i) the finding of a systematic linear relationship between the biceps brachii transverse shear moduli and the corresponding sEMG-RMS values. This was not the case when plotting transverse shear modulus versus the elbow flexion torque production. Therefore, the computation of a hardness index from the slope of individual transverse shear modulus-sEMG-RMS linear relationship was enabled; (ii) It was also found that the higher is the rest shear modulus, the lower is the hardness index, indicating that the transverse shear modulus change during contraction depends on its level at rest. Therefore, this non-invasive technique could be useful in the medical field to explore deep muscles which are unreachable by classical testing methods. It could also be applied for the follow-up of neuromuscular diseases inducing stiffness changes such as in Duchenne muscular dystrophy. © 2004 Published by Elsevier Ltd. Mots-clés: Isometric contraction; Muscle hardness; Shear wave; Surface EMG; Young's modulus; Biomechanics; Disease control; Elastic moduli; Elasticity; Electromyography; Hardness; Neurology; Signal processing; Torque control; Biceps brachii; Isometric contraction; Surface electromyographic signal (sEMG); Transient elastography; Muscle; adult; article; biceps brachii muscle; controlled study; elastography; elbow flexion; electromyography; frequency analysis; hardness; human; human experiment; linear system;
Resonant tunneling of acoustic waves through a double barrier consisting of two phononic crystals Van Der Biest, F., A. Sukhovich, A. Tourin, J. H. Page, B. A. Van Tiggelen, Z. Liu, and M. Fink Europhysics Letters 71, no. 1, 63-69 (2005) Résumé: We present the acoustic analog of resonant tunneling through a double barrier in quantum mechanics. Pairs of identical phononic crystals, in both 2D and 3D, were assembled and separated by a uniform spacer, forming a resonant cavity. The ultrasonic transmission exhibits resonant peaks at frequencies inside the band gaps, where ultrasound tunneling through each phononic crystal occurs. On resonance, the measured group time is large and even predicted to increase exponentially with the thickness of the crystals in the absence of absorption, while off resonance very fast speeds are found. © EDP Sciences.
Time reversal of noise sources in a reverberation room Ribay, G., J. De Rosny, and M. Fink Journal of the Acoustical Society of America 117, no. 5, 2866-2872 (2005) Résumé: Usually, time reversal is studied with pulsed emissions. Here, the properties of time reversal of the acoustic field emitted by noise sources in a reverberation room are studied numerically, theoretically, and experimentally. A time domain numerical simulation of a two-dimensional enclosure shows that the intensity of a time-reversed noise is strongly enhanced right on the initial source position. A theory based on the link that exists between time reversal of noise and the "well-known" time reversal of short pulse is developed. One infers that the focal spot size equals half a wavelength and the signal to noise ratio only depends on the number of transceivers in the time reversal mirror. This last property is characteristic of the time reversal of noise. Experimental results are obtained in a 5 × 3 × 3 m3 reverberation room. The working frequency range varies from 300 Hz to 2 kHz. The ability of the time reversal process to physically reconstruct the image of two noise sources is studied. To this end, care is given to the technique to separate two close random sources, and also to the influence of temperature fluctuations on the focusing quality. © 2005 Acoustical Society of America. Mots-clés: Computer simulation; Image processing; Natural frequencies; Reverberation; Signal to noise ratio; Time domain analysis; Noise sources; Random sources; Time reversal mirrors; Time-reversed noise; Acoustic noise; acoustics; article; noise measurement; priority journal; simulation; technique; theoretical model; time; Acoustics; Models, Theoretical; Noise; Time Factors
Predicting and preventing skull overheating in non invasive brain HIFU treatment protocols Pernot, M., J.-F. Aubry, M. Tanter, and M. Fink AIP Conference Proceedings 754, 147-150 (2005) Résumé: Ultrasound brain therapy is currently limited by the strong phase and amplitude aberrations induced by the heterogeneities of the skull. However the development of aberration correction techniques has made it possible to correct the beam distortion induced by the skull and to produce a sharp focus in the brain. Moreover, using the density of the skull bone that can be obtained with high-resolution CT scans, the corrections needed to produce this sharp focus can be calculated using ultrasound propagation models. We propose here a model for computing the temperature elevation in the skull during High Intensity Focused Ultrasound (HIFU) transcranial therapy. Based on CT scans, the wave propagation through the skull is computed with 3D finite differences wave propagation software. The acoustic simulation is combined with a 3D thermal diffusion code and the temperature elevation inside the skull is computed. Finally, the simulation is validated experimentally by measuring the temperature elevation in several locations of the skull. © 2005 American Institute of Physics.
Adaptive focusing for ultrasonic transcranial brain therapy: First in vivo investigation on 22 sheep Pernot, M., J.-F. Aubry, M. Tanter, A. L. Boch, M. Kujas, and M. Fink AIP Conference Proceedings 754, 174-177 (2005) Résumé: A high power prototype dedicated to trans-skull therapy has been tested in vivo on 22 sheep. The array is made of 300 high power transducers working at 1MHz central frequency and is able to achieve 400 bars at focus in water during five seconds with a 50% percent duty cycle. In the first series of experiments, 10 sheep were treated and sacrificed immediately after treatment. A complete craniotomy was performed on half of the treated animal models in order to get a reference model. On the other half, minimally invasive surgery has been performed: a hydrophone was inserted at a given target location inside the brain through a craniotomy of a few mm2. A time reversal experiment was then conducted through the skull bone with the therapeutic array to treat the targeted point. Thanks to the high power technology of the prototype, trans-skull adaptive treatment could be achieved. In a second series of experiments, 12 animals were divided into three groups and sacrificed respectively one, two or three weeks after treatment. Finally, Magnetic Resonance Imaging and histological examination were performed to confirm tissue damage. © 2005 American Institute of Physics.
Viscoelastic shear properties of in vivo breast lesions measured by MR elastography Sinkus, R., M. Tanter, T. Xydeas, S. Catheline, J. Bercoff, and M. Fink Magnetic Resonance Imaging 23, no. 2 SPEC. ISS., 159-165 (2005) Résumé: Elastography is a technique to assess the viscoelastic properties of tissue by measuring an acoustic wave propagating though the object. Here, the technique is applied in the course of standard MR mammography to 15 patients with different pathologies (six breast cancer cases, six fibroadenoma cases and three mastopathy cases). Low-frequency mechanical waves are coupled longitudinally into the tissue in order to obtain sufficient wave amplitude throughout the entire breast. This leads to the presence of a substantial fraction of compressional waves, which contribute to the total displacement field. It is shown theoretically that the correct evaluation of these contributions from the compressional wave is rather difficult due to the almost incompressible nature of tissue. To overcome this problem, it is proposed to apply the curl-operator to the measured displacement field in order to completely remove contributions from the compressional wave. Results from simulations and a breast phantom demonstrate the feasibility of the technique. The in vivo results show a good separation between breast cancer and benign fibroadenoma utilizing the shear modulus. Breast cancer appears on average 2.2 (P<.001) times stiffer. All breast cancer cases showed a good delineation to the surrounding breast tissue with an average elevation of a factor of 3.3 (P<1.4×10 -6). The results as obtained for the shear viscosity do not indicate to be useful for separating benign from malignant lesions. © 2005 Elsevier Inc. All rights reserved. Mots-clés: Breast lesion; Elastography; Viscoelasticity; amplitude modulation; benign tumor; breast cancer; breast disease; breast fibroadenoma; breast lesion; conference paper; elastography; frequency modulation; human; malignant neoplastic disease; mammography; measurement; nuclear magnetic resonance; pathology; priority journal; simulation; viscoelasticity; viscosity; Acoustics; Breast; Breast Diseases; Breast Neoplasms; Elasticity; Female; Fibroadenoma; Humans; Magnetic Resonance Imaging; Phantoms, Ima
Characterization of subwavelength elastic cylinders with the decomposition of the time-reversal operator: Theory and experiment Minonzio, J.-G., C. Prada, D. Chambers, D. Clorennec, and M. Fink Journal of the Acoustical Society of America 117, no. 2, 789-798 (2005) Résumé: The decomposition of the time-reversal operator provides information on the scattering medium. It has been shown [Chambers and Gautesen, J. Acoust. Soc. Am. 109, 2616-2624 (2001)] that a small spherical scatterer is in general associated with four eigenvalues and eigenvectors of the time-reversal operator. In this paper, the 2D problem of scattering by an elastic cylinder, imbedded in water, measured by a linear array of transducers is considered. In this case, the array response matrix has three nonzero singular values. Experimental results are obtained with linear arrays of transducers and for wires of different diameters smaller that the wavelength. It is shown how the singular value distribution and the singular vectors depend on the elastic velocities c L, c T, the density p of each wire, and on the density ρ 0 and velocity c 0 of the surrounding fluid. These results offer a new perspective towards solution of the inverse problem by determining more than scattering contrast using conventional array processing like that used in medical ultrasonic imaging. © 2005 Acoustical Society of America. Mots-clés: Cylinders (shapes); Decomposition; Eigenvalues and eigenfunctions; Elasticity; Scattering; Transducers; Ultrasonic imaging; Medical ultrasonic imaging; Scattering medium; Subwavelegnth elastic cylinders; Time-reversal operator; Acoustic waves; acoustics; article; decomposition; liquid; mathematical analysis; priority journal; signal processing; transducer; ultrasound; velocity; waveform
Imaging anisotropic and viscous properties of breast tissue by magnetic resonance-elastography Sinkus, R., M. Tanter, S. Catheline, J. Lorenzen, C. Kuhl, E. Sondermann, and M. Fink Magnetic Resonance in Medicine 53, no. 2, 372-387 (2005) Résumé: MR-elastography is a new technique for assessing the viscoelastic properties of tissue. One current focus of elastography is the provision of new physical parameters for improving the specificity in breast cancer diagnosis. This analysis describes a technique to extend the reconstruction to anisotropic elastic properties in terms of a so-called transversely isotropic model. Viscosity is treated as being isotropic. The particular model chosen for the anisotropy is appealing because it is capable of describing elastic shear anisotropy of parallel fibers. The dependence of the reconstruction on the particular choice of Poisson's ratio is eliminated by extracting the compressional displacement contribution using the Helmholtz-Hodge decomposition. Results are presented for simulations, a polyvinyl alcohol breast phantom, excised beef muscle, and measurements in two patients with breast lesions (invasive ductal carcinoma and fibroadenoma). The results show enhanced anisotropic and viscous properties inside the lesions and an indication for preferred fiber orientation. © 2005 Wiley-Liss, Inc. Mots-clés: Anisotropy; Breast cancer; MR-elastography; Steady-state; Viscosity; polyvinyl alcohol; anisotropy; article; breast cancer; breast fibroadenoma; cancer diagnosis; diagnostic accuracy; diagnostic procedure; elastic tissue; elastography; human; image quality; invasive carcinoma; mathematical analysis; nuclear magnetic resonance imaging; phantom; Poisson distribution; viscoelasticity; Algorithms; Anisotropy; Breast; Breast Neoplasms; Computer Simulation; Elasticity; Humans; Image Interpretation, Co
Time reversal acoustics Fink, M., G. Montaldo, and M. Tanter Proceedings - IEEE Ultrasonics Symposium 2, 850-859 (2004) Résumé: An overview of time reversal techniques is presented in this paper. In the first section, we will focus on the ability of using reflecting targets embedded in the body as sources of time reversal waves. Real time tracking and destruction of moving kidney stones will be demonstrated in the case of lithotripsy application. We will show the strong potential of iterative time reversal techniques in multiple targets environments to select and focus in real time on each target of a medium. The ability of iterative time reversal to improve the detection of microcalcifications in a random scattering media (speckle noise) will be also presented. We will show that distorsions induced by sound velocity heterogeneities are compensated by the iterative time reversal technique guaranteeing the maximum pressure to be reached at the target position. In the second section of this paper, we will discuss the time reversal focusing properties observed in dissipative media like skull. We will show that the time reversal focal spot can be strongly degraded as, in such medium, we can no more rely on the time reversal invariance of the wave equation. Important sidelobes appear around the main focus. However, combining time reversal with amplitude compensation techniques allows correction of absorption effects and decreasing of these sidelobes. Application of this coupled technique to high precision brain hyperthermia through the skull will be demonstrated. Beyond these straigthtforward applications of time reversal to spatial focusing of waves through aberrating medium, we will show that time reversal techniques allow also to revisit the concept of piezoelectric transducer designing. Contrary to conventional transducer technology avoiding unwanted reverberations in piezoelectric elements, time reversal can take benefit of strongly reverberating media to increase the transducer efficiency. We will demonstrate that very high pressure fields (1000 Atm.) can be obtained with a few number of transducers connected to reverberating media such as solid waveguides. The dispersive property of waveguides is compensated by time reversal allowing very long coded excitations to be recompressed in very short high amplitude pulses. It leads to a new generation of ultra-compact shock wave lithotripters that used a very small transducer number and to time reversal kaleidoscopes that can replaced 2D array. © 2004 IEEE. Mots-clés: Acoustic wave scattering; Ceramic materials; Hyperthermia therapy; Iterative methods; Light absorption; Piezoelectric transducers; Reverberation; Second harmonic generation; Shock waves; Wave equations; Waveguides; Lithotripsy; Microcalcification; Time reversal techniques; Time reversal waves; Acoustics
Local inversion of transient shear wave propagation for elasticity and viscosity mapping in soft tissues: Theoretical and experimental analysis Bercoff, J., M. Tanter, and M. Fink Proceedings - IEEE Ultrasonics Symposium 3, 2149-2152 (2004) Résumé: Observation of transient shear-wave propagation in soft tissue is of great interest for the study of tissue viscoelastic properties. In previous work, we introduced a technique, called Supersonic Shear Imaging (SSI), able to generate transient shear waves using the acoustic radiation force and image their propagation in real time in soft tissues. Inversion methods were used to recover elasticity from the shear-wave propagation. In this work we present a precise and robust inversion algorithm taking into account not only elastic but also viscous properties of soft tissues. Based on a Voigt model, this algorithm is designed to provided quantitative and local estimation of soft tissue elasticity and viscosity. In a first part, the influence of viscosity on transient shear waves is modeled and analyzed using a 3D analytical formulation of the mechanical Greens function in a viscoelastic medium. It is shown that the spatial and temporal shape of experimental shear waves induced in soft tissues using SSI can only be accurately modeled by taking into account tissue shear viscosity. The respective influences of viscosity, elasticity or diffraction on the shear wave shape are carefully studied and discriminated. In a second part, taking advantage of the previous modeling, a local inverse problem permitting the recovery of shear elasticity and viscosity is presented and validated using the Greens function based simulation tool. The role of viscosity on the accuracy of the elasticity estimation is studied. The influence of out of plane shear propagation on the inversion algorithm is discussed. Finally, in media presenting shear viscoelasticity heterogeneities, finite differences simulations are used to study the spatial resolution of the algorithm and its sensitivity to the signal-to-noise ratio. Experiments on calibrated tissuemimicking phantoms presenting different viscoelastic properties are presented validating the simulation results. © 2004 IEEE. Mots-clés: Shear wave propagation; Soft tissues; Supersonic shear imaging (SSI); Viscosity mapping; Algorithms; Computer simulation; Elasticity; Green's function; Mathematical models; Tissue; Ultrasonic imaging; Vectors; Viscoelasticity; Wave propagation; Shear waves
Prediction of the skull overheating during high intensity focused ultrasound transcranial brain therapy Pernot, M., J.-F. Aubry, M. Tanter, F. Andre, and M. Fink Proceedings - IEEE Ultrasonics Symposium 2, 1005-1008 (2004) Résumé: Ultrasound brain therapy is currently limited by the strong phase and amplitude aberrations induced by the heterogeneities of the skull. However the development of aberration correction techniques has made it possible to correct the beam distortion induced by the skull and to produce a sharp focus in the brain. Moreover, using the density of the skull bone that can be obtained with high-resolution CT scans, the corrections needed to produced this sharp focus can be calculated using ultrasound propagation models. We propose here a model for computing the temperature elevation in the skull during a High Intensity Focused Ultrasound (HIFU) transcranial therapy. Based on CT scans, the wave propagation through the skull is computed with a 3D finite differences wave propagation software. The acoustic simulation is combined with a 3D thermal diffusion code and the temperature elevation inside the skull is computed. Finally, the simulation is experimentally validated by measuring the temperature elevation in several locations of the skull. ©2004 IEEE. Mots-clés: Brain; CT scan; HIFU; Skull bone; Therapy; Ultrasound; Acoustic wave propagation; Bone; Brain; Computer simulation; Computer software; Computerized tomography; CT scan; Skull bone; Temperature elevation; Virtual sources; Ultrasonics
High resolution ultrasonic brain imaging: Noninvasive adaptive focusing based on twin arrays Vignon, F., J. F. Aubry, M. Tanter, and M. Fink Proceedings - IEEE Ultrasonics Symposium 1, 231-234 (2004) Résumé: High resolution transcranial imaging of the brain requires adaptive focusing techniques in order to correct the defocusing effect of the skull bone (absorption, diffusion and refraction of ultrasounds). Here is presented a noninvasive brain imaging device made of two identical "twin" linear arrays located on each side of the skull. It is shown how to separate the respective influence of the two bone windows on the path of an ultrasonic wave going from one array to the other, and estimate at each frequency the attenuation and phase shift locally induced by each of the bone windows. This information is men used to correct, for a wide band signal, the wave fronts that have to be sent through the skull in order to obtain a good focusing inside the skull. Compared to uncorrected wave fronts, the spatial shift of the focal point is cancelled, the width of the focal spot is reduced, and sidelobes level is decreased up to 10dB. Simulated structural transcranial images of a brain model are presented to exhibit the improvement in image quality provided by this new noninvasive adaptive focusing method. © 2004 IEEE. Mots-clés: Adaptive; Brain; Inverse filter; Noninvasive; Ultrasonic imaging; Attenuation; Brain; Image processing; Natural frequencies; Refraction; Signal processing; Ultrasonic imaging; Ultrasonic transducers; Adaptive; Inverse filters; Noninvasive; Noninvasive adaptive focusing; Ultrasonic waves
Measurement of viscoelastic properties of homogeneous soft solid using transient elastography: An inverse problem approach Catheline, S., J.-L. Gennisson, G. Delon, M. Fink, R. Sinkus, S. Abouelkaram, and J. Culioli Journal of the Acoustical Society of America 116, no. 6, 3734-3741 (2004) Résumé: Two main questions are at the center of this paper. The first one concerns the choice of a rheological model in the frequency range of transient elastography, sonoelasticity or NMR elastography for soft solids (20-1000 Hz). Transient elastography experiments based on plane shear waves that propagate in an Agar-gelatin phantom or in bovine muscles enable one to quantify their viscoelastic properties. The comparison of these experimental results to the prediction of the two simplest rheological models indicate clearly that Voigt's model is the better. The second question studied in the paper deals with the feasibility of quantitative viscosity mapping using inverse problem algorithm. In the ideal situation where plane shear waves propagate in a sample, a simple inverse problem based on the Helmholtz equation correctly retrieves both elasticity and viscosity. In a more realistic situation with nonplane shear waves, this simple approach fails. Nevertheless, it is shown that quantitative viscosity mapping is still possible if one uses an appropriate inverse problem that fully takes into account diffraction in solids. © 2004 Acoustical Society of America. Mots-clés: Frequencies; Mapping; Nuclear magnetic resonance spectroscopy; Problem solving; Rheology; Shear waves; Elastography; Soft solids; Viscoelastic properties; Viscosity mapping; Viscoelasticity; agar; gelatin; algorithm; article; cattle; elastography; feasibility study; flow kinetics; measurement; muscle; nuclear magnetic resonance; phantom; priority journal; solid; viscoelasticity; viscosity; echography; elasticity; human; image processing; image quality; instrumentation; mathematical computing; sh
Phononic crystals Page, J. H., A. Sukhovich, S. Yang, M. L. Cowan, F. Van Der Biest, A. Tourin, M. Fink, Z. Liu, C. T. Chan, and P. Sheng Physica Status Solidi (B) Basic Research 241, no. 15, 3454-3462 (2004) Résumé: Phononic crystals are periodic composite materials with lattice spacings comparable to the acoustic wavelength. They are of interest not only because of the profound effects of their periodic structure on wave propagation (e.g., the existence of acoustic band gaps), but also because of potential applications (e.g., their possible role in sound filters, transducer design and acoustic mirrors). In this paper, we summarize recent progress using ultrasonic experiments to investigate both two- and three-dimensional phononic crystals. By measuring the ultrasonic wave field transmitted through slab-shaped samples of different thicknesses, both the dispersion curves and amplitude transmission coefficient can be determined. Because the field is pulsed, the dynamics of the wave fields can also be investigated; this has allowed us to make a systematic study of ultrasonic wave tunneling in phononic crystals. New results on resonant tunneling, focussing and negative refraction phenomena in phononic crystals are also presented. Our data are well explained using Multiple Scattering Theory, giving additional insight into the physical properties and potential applications of these novel materials. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
The Stokes relations linking time reversal and the inverse filter Vignon, F., A. Saez, J. F. Aubry, M. Tanter, and M. Fink Proceedings - IEEE Ultrasonics Symposium 1, 798-800 (2004) Résumé: When focusing through plates or tubes the presence of multiple interfaces induces reflected wave fronts that follow the main wave front Adaptive focusing techniques can be used to cancel the echoes. To illustrate this problem and suggest a solution, the following experiment is performed: two linear arrays of transducers are placed on each side of a titanium plate. Three propagation operators are acquired: transmission from one array to the other, and two reflection operators associated to each array. Here, two adaptive focusing methods have been used to cancel the echoes: first time reversal, using the two arrays cavity surrounding the plate. Second the spatio temporal inverse filter (STIF), inverting the transmission operator: the inverse filter achieves echoes cancellation using only the transmitted fields, whereas time reversal also requires the reflected fields. In fact, transmission and reflection operators are linked by the Stokes relations in a matrix formalism. These relations helps understanding the inverse filter strategy, that deduces the wave front to be emitted from one array to imitate the time reversal cavity using both arrays. The matrix formulation of the Stokes relations also inspires a way to invert the transmission operator by an iterative method, showing a physical link between iterative time reversal and the inverse filter. κ 2004 IEEE. Mots-clés: Adaptive focusing; Inverse filter; Iterative; Time reversal; Adaptive focusing; Emission vectors; Inverse filters; Time reversal; Arrays; Filters (for fluids); Focusing; Green's function; Iterated switching networks; Navier Stokes equations; Plates (structural components); Tubes (components)
3D ultrasound-based dynamic and transient elastography : First in vitro results Bercoff, J., R. Sinkus, M. Tanter, and M. Fink Proceedings - IEEE Ultrasonics Symposium 1, 28-31 (2004) Résumé: The feasibility of performing 3D Dynamic Elastography using an ultrasound based imaging system was described. In addition to providing a low cost system, the ultrasound approach was found to enable the reduction of acquisition time by a factor 300. The visco-elastic maps obtained using this technique were anticipated to be more precise than MR-Elastography as the resolution could lead to a 1.5×1.5×1.5 mm voxel with ultrasound. The potential of this technique for 2D breast elastography for cancer diagnosis was also evaluated. Mots-clés: 3D Dynamic Elastography; 3D Magnetic Resonance (MR) Elastography; Shear anisotropy; Stroboscopic imaging; Algorithms; Anisotropy; Data acquisition; Imaging systems; Stroboscopes; Tissue; Transducers; Vibrations (mechanical); Viscoelasticity; Ultrasonics
Ultrasonic transcranial brain therapy: First in vivo clinical investigation on 22 sheep using adaptive focusing Pernot, M., J.-F. Aubry, M. Tanter, A. L. Boch, M. Kujas, and M. Fink Proceedings - IEEE Ultrasonics Symposium 2, 1013-1016 (2004) Résumé: A high power prototype dedicated to trans-skull therapy has been tested in vivo on 22 sheep. The array is made of 280 high power transducers working at 1MHz central frequency and is able to reach 400 bars at focus in water during five seconds with a 50% percent duty cycle. An echographic array connected to a Philips HDI 1000 system has been inserted in the therapeutic array in order to perform real time monitoring of the treatment. In a first series of experiments, 10 sheep were treated and sacrificed immediately after treatment. A complete craniotomy has been performed on half of the treated animal models in order to get a reference model. On the other animals, a minimally invasive surgery has been performed thanks to a time reversal experiment: a hydrophone was inserted at the target inside the brain thanks to a lmm2 craniotomy. A time reversal experiment was then conducted through the skull bone with the therapeutic array to treat the targeted point. Hyperechogeneicity was clearly visible on the sonographic system for all animals with complete craniotomy. Without craniotomy, the ultrasonic image was distorted but the hydrophone location was visible, allowing a rough positioning of the therapeutic device. A more accurate positioning was then obtained by cross correlating the signals received by a set of elements of the therapeutic device. Thanks to the high power technology of the prototype, trans-skull treatment could be achieved with phase aberration correction and electronic beam steering not only at the geometrical focus but also 2 centimeters away in all directions. In a second series of experiments, 12 animals were divided into three groups and sacrificed respectively one two and three weeks after treatment. The evolution of the targeted region was checked each week thanks to Magnetic Resonance Imaging and CT scans. Finally, histological examination was performed to confirm tissue damage. These in vivo experiments highlight the strong potential of high power transcranial time reversal technology. ©2004 IEEE. Mots-clés: Aberrations; Brain; Magnetic resonance imaging; Mathematical models; Monitoring; Natural frequencies; Surgery; Tissue; Ultrasonic imaging; Ultrasonic transducers; Ultrasonics; Craniotomy; Echographic arrays; Invasive surgery; Trans-skull therapy; Neurology
Time-reversal breaking of acoustic waves in a cavity Bertaix, V., J. Garson, N. Quieffin, S. Catheline, J. Derosny, and M. Fink American Journal of Physics 72, no. 10, 1308-1311 (2004) Résumé: Acoustic time-reversal is a well-established technique that focuses an ultrasonic wave on the location of its source. It is based on the time-reversal invariance of the wave equation and is usually implemented using time-reversal mirrors made up of a hundred of piezoelectric transducers. However, a time-reversal experiment can be performed in a closed cavity (a water-filled beaker) with only one transducer as a pulse-echo system. This easy-to-build and low cost experiment involves students in the general concept of the time-reversal invariance of the wave equation. We show that it also can be adapted to become an ultrasonic time-reversal thermometer. A careful study of the focal point shows a dependence of its position as a function of temperature variations. © 2004 American Association of Physics Teachers.
Relation between time reversal focusing and coherent backscattering in multiple scattering media: A diagrammatic approach De Rosny, J., A. Tourin, A. Derode, B. Van Tiggelen, and M. Fink Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 70, no. 4 2, 046601-1-046601-12 (2004) Résumé: One-channel time reversal (TR) experiments through multiple scattering media were discussed. The hyperresolution and the self-averaging property was described. It was found that the developed formalism leads to a deeper understanding of the role of the ladder and most-crossed diagrams in a TR experiment. Results show that when the initial source and the time reversal point are at the same location, the time-reversed amplitude is twice higher. Mots-clés: Approximation theory; Diffusion; Green's function; Mathematical models; Random processes; Spectroscopy; Statistical methods; Ultrasonic propagation; Paraxial approximation; Spatial focusing; Spatiotemporal focusing; Time reversal (TR); Acoustic wave backscattering
3-D real-time motion correction in high-intensity focused ultrasound therapy Pernot, M., M. Tanter, and M. Fink Ultrasound in Medicine and Biology 30, no. 9, 1239-1249 (2004) Résumé: A method for tracking the 3-D motion of tissues in real-time is combined with a 2-D high-intensity focused ultrasound (US), or HIFU, multichannel system to correct for respiratory motion during HIFU therapy. Motion estimation is based on an accurate ultrasonic speckle-tracking method. A pulse-echo sequence is performed for a subset of the transducers of the phased array. For each of these subapertures, the displacement is estimated by computing the 1-D cross-correlation of the backscattered signals acquired at two different times. The 3-D motion vector is then computed by a triangulation algorithm. This technique is experimentally validated in phantoms moving as fast as 40 mm s -1, and combined with HIFU sequences. A real-time feedback correction of the HIFU beam is achieved by adjusting the delays of each channel. The sonications "locked on target" are interleaved with very short motion-estimation sequences. Finally, in vitro experiments of "locked on target" HIFU therapy are performed in fresh moving tissues. © 2004 World Federation for Ultrasound in Medicine & Biology. Mots-clés: Focused ultrasound; HIFU; Motion tracking; Therapy; High-intensity focused ultrasound (HIFU) therapy; Pulse-echo sequences; Respiratory motion; Ultrasonic speckle-tracking method; Acoustic wave backscattering; Algorithms; Correlation methods; Motion estimation; Respiratory system; Tissue; Transducers; Vectors; Ultrasonics; algorithm; animal tissue; article; breathing mechanics; correlation analysis; feedback system; high intensity focused ultrasound; motion; nonhuman; priority journal; signal tr
Telecommunication in a disordered environment with iterative time reversal Montaldo, G., G. Lerosey, A. Derode, A. Tourin, J. De Rosny, and M. Fink Waves Random Media 14, no. 3, 287-302 (2004) Résumé: We present a method to transmit digital information through a highly scattering medium in a MIMO-MU (multiple input multiple output multiple users) context. It is based on iterations of a time-reversal process, and permits us to focus short pulses, both spatially and temporally, from a base antenna to different users. This iterative technique is shown to be more efficient (lower inter-symbol interference and lower error rate) than classical time-reversal communication, while being computationally light and stable. Experiments are presented: digital information is conveyed from 15 transmitters to 15 receivers by ultrasonic waves propagating through a highly scattering slab. From a theoretical point of view, the iterative technique achieves the inverse filter of propagation in the subspace of non-null singular values of the time-reversal operator. We also investigate the influence of external additive noise, and show that the number of iterations can be optimized to give the lowest error rate. © 2004 IOP Publishing Ltd. Mots-clés: Antenna lobes; Antennas; Digital communication systems; Eigenvalues and eigenfunctions; Iterative methods; Matrix algebra; Signal receivers; Transmitters; Ultrasonic propagation; Multiple input multiple output multiple users; Short pulses; Time reversal method; Electromagnetic wave scattering
Imaging from one-bit correlations of wideband diffuse wave fields Larose, E., A. Derode, M. Campillo, and M. Fink Journal of Applied Physics 95, no. 12, 8393-8399 (2004) Résumé: An imaging technique based on one-bit correlations of wideband diffuse wave fields was discussed. The first step of the imaging process was to retrive the Green's function between two passive sensors from the correlation of the scattered wave fields generated by distant source. It was found that a short ultrasonic pulse, sent through a highly scattering slab, generates a randomly scattered field. The results show that the sound-speed profile of the layered medium can be precisely imaged. Mots-clés: Acoustic waves; Electromagnetic wave scattering; Green's function; Quantum theory; Seismology; Spectroscopic analysis; Spurious signal noise; Ultrasonic waves; Wave propagation; Waveform analysis; Radiative transfer; Random noise; Thermal fluctuations; Time-reversal invariance; Imaging techniques
Time reversal of electromagnetic waves Lerosey, G., J. De Rosny, A. Tourin, A. Derode, G. Montaldo, and M. Fink Physical Review Letters 92, no. 19, 193904-1 (2004) Résumé: A one-channel electromagnetic time-reversal mirror (TRM) was used for investigating the feasibility of time reversal focusing with electromagnetic waves in the GHz range. Two omnidirectional antennas with a frequency of 2.45 GHz and two transceiver circuit boards were also used for the investigations. The baseband signals were time reversed and the wave carriers were phase conjugated in order to avoid digitizing the radio signals at GHz frequencies. The circuit boards demodulated the radio frequency signal back to the baseband. The frequency bandwidth and the spectral correlations determined the quality of focusing. Mots-clés: Analog to digital conversion; Bandwidth; Correlation methods; Demodulation; Light scattering; Light transmission; Low pass filters; Mirrors; Monochromators; Signal receivers; Signal to noise ratio; Transceivers; Ultrasonic effects; Wireless telecommunication systems; Phase conjugation; Quasimonochromatic signals; Spectral correlations; Time reversal mirrors (TRM); Antenna radiation
Real-time focusing using an ultrasonic one channel time-reversal mirror coupled to a solid cavity Quieffin, N., S. Catheline, R. K. Ing, and M. Fink Journal of the Acoustical Society of America 115, no. 5 I, 1955-1960 (2004) Résumé: Focusing and beam steering is achieved by using a time-reversal process and a single transducer coupled to a solid cavity that is immersed in water. This low-cost technique makes it possible to focus acoustic energy anywhere on a 3D domain with a spatio-temporal resolution comparable to that of multiple transducers array. A short pulse is emitted from a transducer stuck at the surface of the solid cavity. The multiple-scattered field is measured in front of the solid cavity using a hydrophone needle at a reference point. This signal is then time reversed and remitted by the transducer. Around the reference point, one can observe a spatio-temporal recompression. The sidelobe level as well as the focal width no longer depend on the transducer aperture but on the dimensions of the solid cavity and the multiple paths covered by the acoustic waves in the solid. Moreover, it is shown how the experimental impulse responses on the front face of the cavity can be used to control the emitting ultrasonic field. This "synthetic time-reversal" technique is shown to be as powerful as a real time-reversal process. © 2004 Acoustical Society of America. Mots-clés: Arrays; Focusing; Hydrophones; Mirrors; Ultrasonic transducers; Spatio-temporal recompression; Time reversal mirrors; Ultrasonic testing; acoustics; acoustics; article; diffraction; mathematical analysis; pressure; priority journal; solid; time; ultrasound; ultrasound transducer
Temperature estimation using ultrasonic spatial compound imaging Pernot, M., M. Tanter, J. Bercoff, K. R. Waters, and M. Fink IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 51, no. 5, 606-615 (2004) Résumé: The feasibility of temperature estimation during high-intensity focused ultrasound therapy using pulseecho diagnostic ultrasound data has been demonstrated. This method is based upon the measurement of thermally-induced modifications in backscattered RF echoes due to thermal expansion and local changes in the speed of sound. It has been shown that strong ripple artifacts due to the thermo-acoustic lens effect severely corrupt the temperature estimates behind the heated region. We propose here a new imaging technique that improves the temperature estimation behind the heated region and reduces the variance of the temperature estimates in the entire image. We replaced the conventional beamforming on transmit with multiple steered plane wave insonifications using several subapertures. A two-dimensional temperature map is estimated from axial displacement maps between consecutive RF images of identically steered plane wave insonifications. Temperature estimation is then improved by averaging the two-dimensional maps from the multiple steered plane wave insonincations. Experiments were conducted in a tissue-mimicking gelatin-based phantom and in fresh bovine liver. Mots-clés: Backscattered signals; Plane wave insonification; Ultrasound therapy; Backscattering; Extrapolation; Image quality; Medical applications; Medical imaging; Temperature distribution; Thermal expansion; Vectors; Ultrasonic imaging
Sonic boom in soft materials: The elastic Cerenkov effect Bercoff, J., M. Tanter, and M. Fink Applied Physics Letters 84, no. 12, 2202-2204 (2004) Résumé: An experimental evidence of an elastic sonic boom in soft materials was reported. The experimental method was based on the ultrasonic remote generation, inside soft media, of a supersonic moving source radiating shear waves in a Mach cone. The sonic boom in soft materials was found to be analogus to the Cerenkov electromagnetic radiation emitted by a beam of charged particles moving at a speed greater than the speed of light. It was suggested that intense shear wave radiated in soft materials are sensitive to medium elasticity inhomogeneities. Mots-clés: Backscattering; Charged particles; Elasticity; Electromagnetic wave propagation; Electromagnetic waves; Piezoelectric transducers; Shear waves; Ultrasonic waves; Cerenkov effects; Mach waves; Sonic booms; Soft magnetic materials
Revisiting iterative time reversal processing: Application to detection of multiple targets Montaldo, G., M. Tanter, and M. Fink Journal of the Acoustical Society of America 115, no. 2, 776-784 (2004) Résumé: The iterative time reversal processing represents a high speed and easy way to self-focus on the strongest scatterer in a multitarget medium. However, finding weaker scatterers is a more difficult task that can be solved by computing the eigenvalue and eigenvector decomposition of the time reversal operator, the so-called DORT method. Nevertheless, as it requires the measurement of the complete interelements response matrix and time-consuming computation, the separation of multiple targets may not be achieved in real time. In this study, a new real time technique is proposed for multitarget selective focusing that does not require the experimental acquisition of the time reversal operator. This technique achieves the operator decomposition using a particular sequence of filtered waves propagation instead of computational power. Due to its simplicity of implementation, this iterative process can be achieved in real time. This high speed selective focusing is experimentally demonstrated by detecting targets through a heterogeneous medium and in a speckle environment. A theoretical analysis compares this technique to the DORT formalism. © 2004 Acoustical Society of America. Mots-clés: Acoustic wave propagation; Eigenvalues and eigenfunctions; Iterative methods; Matrix algebra; Problem solving; Multiple target detection; Time reversal processing; Acoustic wave scattering; acoustics; algorithm; article; calculation; comparative study; filter; priority journal; sound detection; technique; theory; velocity
Real time inverse filter focusing through iterative time reversal Montaldo, G., M. Tanter, and M. Fink Journal of the Acoustical Society of America 115, no. 2, 768-775 (2004) Résumé: In order to achieve an optimal focusing through heterogeneous media we need to build the inverse filter of the propagation operator. Time reversal is an easy and robust way to achieve such an inverse filter in nondissipative media. However, as soon as losses appear in the medium, time reversal is not equivalent to the inverse filter anymore. Consequently, it does not produce the optimal focusing and beam degradations may appear. In such cases, we showed in previous works that the optimal focusing can be recovered by using the so-called spatiotemporal inverse filter technique. This process requires the presence of a complete set of receivers inside the medium. It allows one to reach the optimal focusing even in extreme situations such as ultrasonic focusing through human skull or audible sound focusing in strongly reverberant rooms. But, this technique is time consuming and implied fastidious numerical calculations. In this paper we propose a new way to process this inverse filter focusing technique in real time and without any calculation. The new process is based on iterative time reversal process. Contrary to the classical inverse filter technique, this iteration does not require any computation and achieves the inverse filter in an experimental way using wave propagation instead of computational power. The convergence from time reversal to inverse filter during the iterative process is theoretically explained. Finally, the feasibility of this iterative technique is experimentally demonstrated for ultrasound applications. © 2004 Acoustical Society of America. Mots-clés: Acoustic wave propagation; Focusing; Iterative methods; Ultrasonics; Beam degradations; Real time inverse filters; Acoustic devices; acoustics; absorption; article; calculation; feasibility study; filter; inverse filter; priority journal; sound; sound transmission; ultrasound
The role of the coupling term in transient elastography Sandrin, L., D. Cassereau, and M. Fink Journal of the Acoustical Society of America 115, no. 1, 73-83 (2004) Résumé: The transient radiation of low-frequency elastic waves through isotropic and homogeneous soft media is investigated using the Green's function approach. A careful analysis of the coupling term is performed and yields the introduction of a very near field region in which its amplitude behaves as 1/r. To address the calculation of impulse responses, a simplified Green's function is proposed for semi-infinite media and compared to exact solutions. Impulse response calculations are successfully compared with experimental measurements obtained for circular radiators of different diameters using transient elastography. Results presented in this paper provide a better understanding of the role of the coupling term in elastography and should be used to compensate diffraction and coupling effects observed in transient elastography. © 2004 Acoustical Society of America. Mots-clés: Acoustic wave diffraction; Green's function; Coupling effects; Elastography; Elastic waves; acoustics; article; calculation; elastography; mathematical model; measurement; priority journal; radiation; Elastic Tissue; Elasticity; Humans; Models, Theoretical; Phantoms, Imaging; Transducers; Ultrasonography
Feasibility of real-time motion correction for H.I.F.U applications Pernot, M., M. Tanter, and M. Fink Proceedings of the IEEE Ultrasonics Symposium 1, 998-1001 (2003) Résumé: Though HIFU may offer a practical alternative to conventional surgery for a range of abdominal tumors, patient motion (particularly respiratory motion) should be monitored and corrected. We propose here a new generation of multi-channel HIFU systems able to track and correct in real time 3D motion of tissues. The feasibility of a 3D real time motion tracking and feedback for the H.I.F.U. beam focal spot location is demonstrated. The process is based on an accurate ultrasonic speckle tracking method for following and compensating the 3D motion of the tumor. Experiments were conducted with an electronically focused phased array made of 200 elements. This unique system is used both for motion tracking and feedback electronic steering of the HIFU beam. The displacement estimation is based on the correlation of the RF signals at two different times. A pulse-echo sequence is performed for a set of transmit transducers of the phased array. The complete 3D motion estimation requires to use at least three sub-apertures on the large phased array. This motion tracking technique has been experimentally validated in phantoms moving as fast as 50 mm/s. The motion tracking sequences are interleaved with HIFU sequences at high frame rate. The HIFU sonication is interrupted every 100 ms in order to allow motion estimation performed in a few ms. This provides a real time feedback for the HIFU beam steering correction. A maximum duty cycle of about 80% was performed experimentally. HIFU experiments combined with 3D real time motion correction conducted in fresh tissues samples will be presented. Mots-clés: Algorithms; Biological organs; Computerized tomography; Electronic equipment; Real time systems; Surgery; Tissue; Transducers; Intensity modulated radiation therapy (IMRT); Motion tracking; Sonication; Ultrasonics
Measurement of elastic nonlinearity of soft solid with transient elastography Catheline, S., J.-L. Gennisson, and M. Fink Journal of the Acoustical Society of America 114, no. 6 I, 3087-3091 (2003) Résumé: Transient elastography is a powerful tool to measure the speed of low-frequency shear waves in soft tissues and thus to determine the second-order elastic modulus μ (or the Young's modulus E). In this paper, it is shown how transient elastography can also achieve the measurement of the nonlinear third-order elastic moduli of an Agar-gelatin-based phantom. This method requires speed measurements of polarized elastic waves measured in a statically stressed isotropic medium. A static uniaxial stress induces a hexagonal anisotropy (transverse isotropy) in solids. In the special case of uniaxially stressed isotropic media, the anisotropy is not caused by linear elastic coefficients but by the third-order nonlinear elastic constants, and the medium recovers its isotropic properties as soon as the uniaxial stress disappears. It has already been shown how transient elastography can measure the elastic (second-order) moduli in a media with transverse isotropy such as muscles. Consequently this method, based on the measurement of the speed variations of a low-frequency (50-Hz) polarized shear strain waves as a function of the applied stress, allows one to measure the Landau moduli A, B, C that completely describe the third-order nonlinearity. The several orders of magnitude found among these three constants can be justified from the theoretical expression of the internal energy. © 2003 Acoustical Society of America. Mots-clés: Anisotropy; Elastic moduli; Elasticity; Stress analysis; Tissue; Soft solids; Speed measurement; Third-order nonlinear elastic constants; Transient elastography; Shear waves; agar; gelatin; acoustics; anisotropy; article; calculation; elasticity; elastography; energy; mathematical analysis; phantom; priority journal; soft tissue; solid; theory; Elasticity; Humans; Mathematical Computing; Nonlinear Dynamics; Phantoms, Imaging; Shear Strength; Transducers; Ultrasonography; Vibration
Study of elastic non linearity of soft solids with transient elastography Jacob, X., J.-L. Gennisson, S. Catheline, M. Tanter, C. Barrière, D. Royer, and M. Fink Proceedings of the IEEE Ultrasonics Symposium 1, 660-663 (2003) Résumé: An overview of three experiments that allow to illustrate and quantify the nonlinear behavior of soft tissue phantoms was presented. In the first experiment, a static stresss was applied on a sample. The change on the shear wave speed characterized the nonlinear elastic Landau moduli. In the second one, an experimental observation of a shock shear wave was presented. In the third one, the interaction between two plane transverse waves with frequencies ω1 and ω2 was studied. Mots-clés: Anisotropy; Computer simulation; Elasticity; Harmonic analysis; Shear waves; Tissue; Transients; Tumors; Displacements; Elastography; Magnetic resonance elastography; Sonoelastography; Ultrasonics
Ultrasonically induced necrosis through the rib cage based on adaptive focusing: Ex vivo experiments Pernot, M., J.-F. Aubry, M. Tanter, and M. Fink Proceedings of the IEEE Ultrasonics Symposium 1, 833-836 (2003) Résumé: Ex vivo experiments have been conducted through excised lamb rib cages, with bone, cartilage, muscle and skin. The ribs were placed between a hydrophone and a programmable sparse array made of 200 high power transducers working at 1 MHz central frequency. First, adaptive focusing through ribs has been experimentally studied at low power. Without any correction, the pressure fields in the focal plane were affected by both inhomogeneous attenuation and phase distortion and three main effects were observed: a mean 2 mm shift of the main lobe, a mean 1.25 mm spreading in the half width of the main lobe and up to 20 dB increase in the secondary lobe level. Three adaptive focusing techniques were tested with continuous waves: phase shift, time reversal and time reversal coupled with amplitude compensation. We show that time reversal is more appropriate, as it minimizes the heating of the ribs by naturally sonicating between the ribs. It is also shown that a non invasive technique could be implemented by using the imaging capabilities of the therapeutic array. Mots-clés: Absorption; Diseases; Hydrophones; Hyperthermia therapy; Medical imaging; Phase shift; Real time systems; Tissue; Transducers; Tumors; Electronic steering; Necrosis; Programmable sparse array; Sonication; Ultrasonics
Sound focusing in rooms. II. The spatio-temporal inverse filter Yon, S., M. Tanter, and M. Fink Journal of the Acoustical Society of America 114, no. 6 I, 3044-3052 (2003) Résumé: The potential of time reversal processing for room acoustics has been extensively investigated in the companion of this paper [J. Acoust. Soc. Am. 113(3), 1533-1543 (2003)]. In particular, a simple implementation of a loudspeaker time reversal antenna able to take advantage of the multiple reflections in reverberating rooms demonstrates its potential for audible range acoustics while improving focusing both in space and time. However, loss of information (e.g., sound absorption in walls or nonequalized bandwidths of the loudspeakers) during a time reversal experiment degrades the quality of time reversal focusing. In this paper, a more sophisticated technique called spatio-temporal inverse filtering is investigated that achieves time and space deconvolution of the propagation operator between the loudspeakers antenna and a set of microphones embedded inside the insonified volume. Theoretical and experimental comparisons between time reversal and inverse filter focusing are presented. Finally, advantages and limitations of both focusing approaches are highlighted. © 2003 Acoustical Society of America. Mots-clés: Acoustic wave propagation; Acoustic wave reflection; Antennas; Bandwidth; Loudspeakers; Microphones; Inverse filters; Spatio-temporal inverse filtering; Acoustic waves; acoustics; acoustics; antenna; article; comparative study; controlled study; filter; frequency modulation; microphone; priority journal; sound; sound transmission; space; theory
Observation of Shock Transverse Waves in Elastic Media Catheline, S., J.-L. Gennisson, M. Tanter, and M. Fink Physical Review Letters 91, no. 16, 1643011-1643014 (2003) Résumé: A shock transverse wave propagation in an elastic medium was studied by using Burger's equation. The shock formation was observed over a distance of less than a few wavelengths. The results showed that the shock distance increases when the wave amplitude is decreased. Mots-clés: Algorithms; Boundary conditions; Computer simulation; Equations of motion; Mathematical models; Shear waves; Wave propagation; Shock transverse wave propagation; Shock waves
High power transcranial beam steering for ultrasonic brain therapy Pernot, M., J.-F. Aubry, M. Tanter, J.-L. Thomas, and M. Fink Physics in Medicine and Biology 48, no. 16, 2577-2589 (2003) Résumé: A sparse phased array is specially designed for non-invasive ultrasound transskull brain therapy. The array is made of 200 single elements corresponding to a new generation of high power transducers developed in collaboration with Imasonic (Besançon, France). Each element has a surface of 0.5 cm2 and works at 0.9 MHz central frequency with a maximum 20 W cm-2 intensity on the transducer surface. In order to optimize the steering capabilities of the array, several transducer distributions on a spherical surface are simulated: hexagonal, annular and quasi-random distributions. Using a quasi-random distribution significantly reduces the grating lobes. Furthermore, the simulations show the capability of the quasi-random array to electronically move the focal spot in the vicinity of the geometrical focus (up to ±15 mm). Based on the simulation study, the array is constructed and tested. The skull aberrations are corrected by using a time reversal mirror with amplitude correction achieved thanks to an implantable hydrophone, and a sharp focus is obtained through a human skull. Several lesions are induced in fresh liver and brain samples through human skulls, demonstrating the accuracy and the steering capabilities of the systems. Mots-clés: Computer simulation; Hydrophones; Transducers; Ultrasonic applications; High power transducers; Brain; accuracy; article; brain injury; controlled study; echoencephalography; electronics; equipment design; human; nonhuman; priority journal; process model; process optimization; skull; surface property; ultrasound therapy; ultrasound transducer; Brain; Brain Diseases; Computer Simulation; Computer-Aided Design; Equipment Design; Equipment Failure Analysis; Heat; Humans; Liver; Models, Biological;
Resolution enhancement and separation of reverberation from target echo with the time reversal operator decomposition Folégot, T., C. Prada, and M. Fink Journal of the Acoustical Society of America 113, no. 6, 3155-3160 (2003) Résumé: Time reversal operator (TRO) decompositions are performed in a model of an ocean wave guide containing a target and having different kinds of bottom. The objective is to study the effects of bottom reverberation and absorption by means of ultrasonic experiments. It is shown experimentally that the echo from a target can be separated from the bottom reverberation. Reverberation eigenvectors are back propagated in the wave guide leading to focus on the bottom. An amplitude correction is applied to both reverberation and signal eigenvectors to compensate for bottom absorption and thus to improve target resolution. © 2003 Acoustical Society of America. Mots-clés: Acoustic wave absorption; Backpropagation; Eigenvalues and eigenfunctions; Mathematical operators; Ultrasonic applications; Water waves; Target resolution; Reverberation; poly(methyl methacrylate); water; acoustics; absorption; acoustics; article; Fourier transformation; priority journal; sea; signal noise ratio; time; ultrasound
Field fluctuation spectroscopy in a reverberant cavity with moving scatterers De Rosny, J., P. Roux, M. Fink, and J. H. Page Physical Review Letters 90, no. 9, 094302/1-094302/4 (2003) Résumé: Ultrasonic waves were used to investigate the fluctuations of the wave field due to the motion of scatterers inside a static reverberant cavity. A theory, in the limit of large scattering mean free path compared to the largest cavity dimension, that gives an excellent description of the experimental results was developed. By showing how the field auto-correlation function depends on the scattering mean free path of the waves and motion of the scatterers, the principles of a new technique in field fluctuation spectroscopy, diffusing reverberant acoustic wave spectroscopy (DRAWS) was demonstrated. Mots-clés: Calculations; Correlation methods; Diffusion; Spectroscopic analysis; Stainless steel; Stepping motors; Ultrasonic reflection; Ultrasonic scattering; Water tanks; Acoustic wave field; Acoustic wave spectroscopy; Elastic mean free path; Field fluctuation spectroscopy; Fish monitoring; Stainless steel ball; Ultrasonic propagation
Sound focusing in rooms: The time-reversal approach Yon, S., M. Tanter, and M. Fink Journal of the Acoustical Society of America 113, no. 3, 1533-1543 (2003) Résumé: New perspectives in audible range acoustics, such as virtual sound space creation and active noise control, rely on the ability of the rendering system to recreate precisely a desired sound field. This ability to control sound in a given volume of a room is directly linked to the capacity to focus acoustical energy both in space and time. However, sound focusing in rooms remains a complicated problem, essentially because of the multiple reflections on obstacles and walls occurring during propagation. In this paper, the technique of time-reversal focusing, well known in ultrasound, is experimentally applied to audible range acoustics. Compared to classical focusing techniques such as delay law focusing, time reversal appears to considerably improve quality of both temporal and spatial focusing. This so-called super-resolution phenomenon is due to the ability of time reversal to take into account all of the different sound paths between the emitting antenna and the focal point, thus creating an adaptive spatial and temporal matched filter for the considered propagation medium. Experiments emphasize the strong robustness of time-reversal focusing towards small modifications in the medium, such as people in motion or temperature variations. Sound focusing through walls using the time-reversal approach is also experimentally demonstrated. © 2003 Acoustical Society of America. Mots-clés: Acoustic variables control; Acoustic wave propagation; Acoustics; Time-reversal focusion; Acoustic noise measurement; acoustics; acoustics; article; energy; motion; noise reduction; priority journal; sound; space; technique; temperature; time; Acoustics; Auditory Perception; Humans; Noise; Social Environment; Sound Spectrography
Green's function estimation using secondary sources in a shallow water environment Roux, P., and M. Fink Journal of the Acoustical Society of America 113, no. 3, 1406-1416 (2003) Résumé: This work provides a new way to measure the Green's function between two points in an acoustic channel without emitting a pulse by any of the two points. The Green's function between A and B is obtained from a set of secondary sources in the guide by averaging either the correlation or the convolution of the signals received in A and B. A theoretical approach based on mode propagation in a monochromatic regime is presented. Results are then extended to the time domain. Estimation of the Green's function is performed numerically in a range-independent and a range-dependent environment. Application to discreet acoustic communications is discussed. © 2003 Acoustical Society of America. Mots-clés: Correlation methods; Green's function; Time domain analysis; Water; Acoustic channels; Acoustic wave propagation; water; acoustics; acoustics; analytic method; article; correlation analysis; mathematical analysis; priority journal; sound transmission; theory; time
Taking advantage of multiple scattering to communicate with time-reversal antennas Derode, A., A. Tourin, J. De Rosny, M. Tanter, S. Yon, and M. Fink Physical Review Letters 90, no. 1, 014301/1-014301/4 (2003) Résumé: An overview is given of the experimental demonstration that high-order scattering in a disordered medium can help by increasing the information transfer rate, especially if the time-reversal technique is used to naturally focus the different bistreams onto the receivers. The first key parameter in the experiment is the number of independent focal spots that can be created by the transmitting array in the receiving plane. The second key parameter is the number of uncorrelated frequencies within the bandwidth, which governs the peak-to-noise ratio on each receiver. Mots-clés: Antenna arrays; Communication channels (information theory); Data communication systems; Decoding; Eigenvalues and eigenfunctions; Electromagnetic wave propagation; Fourier transforms; Matrix algebra; Signal receivers; Ultrasonic devices; Vectors; Wireless telecommunication systems; Time reversal antennas; Ultrasonic antennas; Electromagnetic wave scattering
Experimental demonstration of noninvasive transskull adaptive focusing based on prior computed tomography scans Aubry, J.-F., M. Tanter, M. Pernot, J.-L. Thomas, and M. Fink Journal of the Acoustical Society of America 113, no. 1, 84-93 (2003) Résumé: Developing minimally invasive brain surgery by high-intensity focused ultrasound beams is of great interest in cancer therapy. However, the skull induces strong aberrations both in phase and amplitude, resulting in a severe degradation of the beam shape. Thus, an efficient brain tumor therapy would require an adaptive focusing, taking into account the effects of the skull. In this paper, we will show that the acoustic properties of the skull can be deduced from high resolution CT scans and used to achieve a noninvasive adaptive focusing. Simulations have been performed with a full 3-D finite differences code, taking into account all the heterogeneities inside the skull. The set of signals to be emitted in order to focus through the skull can thus be computed. The complete adaptive focusing procedure based on prior CT scans has been experimentally validated. This could have promising applications in brain tumor hyperthermia but also in transcranial ultrasonic imaging. © 2003 Acoustical Society of America. Mots-clés: Aberrations; Computer simulation; Computerized tomography; Neurosurgery; Oncology; Brain tumor; Ultrasonic imaging; tomography; acoustics; adaptation; article; brain tumor; calculation; computer assisted tomography; Doppler echography; human; human tissue; hyperthermia; image analysis; priority journal; simulation; skull; sound detection; ultrasound; Acoustics; Brain Neoplasms; Computer Simulation; Echoencephalography; Humans; Image Processing, Computer-Assisted; Imaging, Three-Dimensional; Math
3D spatial resolution enhancement through environmental effects with the time reversal operator decomposition Folégot, T., C. Prada, and M. Fink Oceans Conference Record (IEEE) 1, 65-71 (2002) Résumé: Time Reversal Operator (TRO) Decompositions are performed in a wave-guide using different kinds of bottom. The purchase objective is to study the effects of bottom reverberation and absorption by mean of ultrasonic experiments. Amplitude compensation is proposed to improve the resolution of the system and signal to noise ratio at target. Time dependent reverberation eigenvectors are back propagated in the medium and the conditions of focus on the bottom are discussed. A 3D-TRO is also constructed using an original array configuration which take huge advantage of the multipath propagation in the wave-guide and allows selective multi target 3D-detection. The results could be used to increase echo levels in shallow water active detection or mine countermeasures. Mots-clés: Backpropagation; Eigenvalues and eigenfunctions; Environmental impact; Multipath propagation; Reverberation; Signal to noise ratio; Ultrasonics; Waveguides; Time reversal operators (TRO); Marine applications
Time reversal techniques in ultrasonic nondestructive testing of scattering media Prada, C., E. Kerbrat, D. Cassereau, and M. Fink Inverse Problems 18, no. 6, 1761-1773 (2002) Résumé: Time reversal techniques are adaptive methods that can be used in nondestructive evaluation to improve flaw detection through inhomogeneous and scattering media. Two techniques are presented: the iterative time reversal process and the DORT (French acronym for decomposition of the time reversal operator) method. In pulse echo mode, iterative time reversal mirrors allow one to accurately control wave propagation and focus selectively on a defect reducing the speckle noise due to the microstructure contribution. The DORT method derives from the mathematical analysis of the iterative time reversal process. Unlike time reversal mirrors, it does not require programmable generators and allows the simultaneous detection and separation of several defects. These two procedures are presented and applied to detection in titanium billets where the grain structure renders detection difficult. Then, they are combined with the simulation code PASS (phased array simulation software) to form images of the samples. Mots-clés: Adaptive systems; Computer simulation; Computer software; Iterative methods; Microstructure; Mirrors; Nondestructive examination; Speckle; Ultrasonic testing; Time reversal techniques; Inverse problems
Ultrasonic nondestructive testing of scattering media using the decomposition of the time-reversal operator Kerbrat, E., C. Prada, D. Cassereau, and M. Fink IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 49, no. 8, 1103-1113 (2002) Résumé: In ultrasonic nondestructive testing, the iterative time-reversal process is an adaptive technique that can be used to detect flaws in complex samples with a large array of transducers. The decomposition of the time-reversal operator (D.O.R.T.) method is a detection technique that is derived from the mathematical analysis of the iterative time-reversal process. Contrary to time-reversal techniques, the D.O.R.T. method does not require programmable generators, and it allows the simultaneous detection and separation of several defects. In this paper, the method is applied to a Ti6-4 titanium cylindrical sample to separate the echo of a defect from the speckle due to microstructure contribution. The grain structure of this titanium alloy makes detection very difficult and, for large depths, conventional techniques do not allow the detection of small flaws with a satisfactory signal-to-noise ratio. The efficiency of the D.O.R.T. method to detect a flat bottom hole with a diameter of 0.4 mm located at a depth of 140 mm in a titanium alloy sample is shown. Mots-clés: Acoustic wave scattering; Mathematical operators; Microstructure; Signal to noise ratio; Titanium alloys; Ultrasonic transducers; Time-reversal operators; Acoustic emission testing
Depth and range shifting of a focal spot using a time-reversal mirror in an acoustic waveguide Conti, S., P. Roux, and M. Fink Applied Physics Letters 80, no. 19, 3647-3649 (2002) Résumé: We present a technique based on time reversal to focus an acoustic field at any depth and range in a waveguide. We take advantage of the signal received from an acoustic beacon in the guide to build a time-reversed modified version of the field that refocuses at a different point in the waveguide. This method is based on the application of the images theorem in the guide and, as in the classical time-reversal experiment, it does not require a priori knowledge of the waveguide characteristics. Ultrasonic laboratory experiments and underwater acoustic simulations are presented and compared to classical time-reversal focusing results. © 2002 American Institute of Physics. Mots-clés: Acoustic simulations; Acoustic waveguides; Focal spot; Laboratory experiments; Priori knowledge; Time-reversal; Time-reversal focusing; Time-reversed; Waveguide characteristic; Acoustic fields; Experiments; Ultrasonic applications; Waveguides; Underwater acoustics
Detection of cracks in a thin air-filled hollow cylinder by application of the DORT method to elastic components of the echo Kerbrat, E., D. Clorennec, C. Prada, D. Royer, D. Cassereau, and M. Fink Ultrasonics 40, no. 1-8, 715-720 (2002) Résumé: The DORT method (Décomposition de l'Opérateur de Retournement Temporel in French) is a scattering analysis technique which uses arrays of transducers. This method is efficient for detection of selective focusing on point-like scatterers. It has been also applied to analyze the scattering by an air-filled cylindrical steel shell immersed in water. It was shown that the diagonalization of the time reversal operator allows us to separate the different elastic components of the scattered field. Here, we apply the method to detect flaws in hollow cylinders. In this case, the dominant components are the three circumferential waves (A0, A1 and S0 Lamb modes). Each Lamb mode corresponds to an invariant of the time reversal operator. The dispersion curves of these waves are calculated from these invariants. Resonance frequencies of the shell are deduced from the frequency dependence of the eigenvalues of the time reversal operator. It is shown that the presence of a crack (0.2 mm in depth) affects significantly the eigenvalue distribution of the time reversal operator. Thus, the DORT method offers a new means for detecting defects in a shell. © 2002 Elsevier Science B.V. All rights reserved. Mots-clés: Crack; DORT method; Hollow cylinder; Lamb waves; Nondestructive evaluation; Acoustic wave scattering; Cracks; Cylinders (shapes); Eigenvalues and eigenfunctions; Natural frequencies; Nondestructive examination; Transducers; Lamb waves; Acoustic wave propagation
Time reversal versus phase conjugation in a multiple scattering environment Derode, A., A. Tourin, and M. Fink Ultrasonics 40, no. 1-8, 275-280 (2002) Résumé: We present experimental results on the reversibility of ultrasound in a multiple scattering medium. An ultrasonic pulsed wave is transmitted from a point source to a 128-element receiving array through 2D samples with various thickness. The samples consist of random collections of parallel steel rods immersed in water. The scattered waves are recorded, time reversed and sent back into the medium. The time-reversed waves are converging back to their source and the quality of spatial and temporal focusing on the source is related to the second-order moments of the scattered wave (correlation) in time and in space. Experimental results show that it is possible to obtain a robust estimation of the correlations on a single realisation of disorder, taking advantage of the wide frequency bandwidth. The spatial resolution of the system is only limited by the correlation length of the scattered field, and no longer by diffraction. Moreover, successful time-reversal focusing using a single element instead of an array is possible, whereas a one-channel monochromatic phase conjugation fails. The efficiency of broad-band time reversal compared to monochromatic phase conjugation lies in the number of 'information grains' in the frequency bandwidth. © 2002 Elsevier Science B.V. All rights reserved. Mots-clés: Multiple scattering; Phase conjugation; Time reversal; Bandwidth; Focusing; Monochromators; Natural frequencies; Optical correlation; Optical phase conjugation; Optical resolving power; Robustness (control systems); Ultrasonic waves; Multiple scattering; Ultrasonic scattering
Boosting sonoluminescence with a high-intensity ultrasonic pulse focused on the bubble by an adaptive array Thomas, J.-L., Y. Forterre, and M. Fink Physical Review Letters 88, no. 7, 743021-743024 (2002) Résumé: A new experimental approach for boosting sonoluminescence was presented, where an high intensity ultrasonic pulse of high frequency was adaptively focused on the bubble during the collapse. A pressure pulse of 0.7 MPa doubled the flash intensity using an array of eight transmitters. A brightness gain of a factor of 2 was obtained, which was limited only by the power of the transducers. Mots-clés: Bubbles (in fluids); Focusing; Fusion reactions; Photons; Pressure effects; Transmitters; Ultrasonic waves; Single-bubble sonoluminescence (SBSL); Ultrasonic pulses; Sonoluminescence
Ultrasound shock wave generator with one-bit time reversal in a dispersive medium, application to lithotripsy Montaldo, G., P. Roux, A. Derode, C. Negreira, and M. Fink Applied Physics Letters 80, no. 5, 897-899 (2002) Résumé: The building of high-power ultrasonic sources from piezoelectric ceramics is limited by the maximum voltage that the ceramics can endure. We have conceived a device that uses a small number of piezoelectric transducers fastened to a cylindrical metallic waveguide. A one-bit time- reversal operation transforms the long-lasting low-level dispersed wave forms into a sharp pulse, thus taking advantage of dispersion to generate high-power ultrasound. The pressure amplitude that is generated at the focus is found to be 15 times greater than that achieved with comparable standard techniques. Applications to lithotripsy are discussed and the destructive efficiency of the system is demonstrated on pieces of chalk. © 2002 American Institute of Physics. Mots-clés: Dispersive medium; High power ultrasound; High-power ultrasonics; Lithotripsy; Long lasting; Metallic waveguide; Pressure amplitudes; Shock wave generator; Time reversal; Wave forms; Building materials; Ceramic materials; Piezoelectric ceramics; Piezoelectricity; Ultrasonics; Dispersion (waves)
Mathematical foundations of the time reversal mirror Bardos, C., and M. Fink Asymptotic Analysis 29, no. 2, 157-182 (2002) Résumé: In the present paper a mathematical analysis of the "time reversal mirror" (cf. [4,9,10]) is given. As a first step of a more detailed program, the emphasis is put on phenomena which are described by the genuine acoustic equation with Dirichlet or "impedance" boundary conditions. An ideal situation is first considered then relation between the question of the local decay of energy and the accuracy of the method are exploited. The positive effect of the ergodicity is explained and eventually comparison with control theory approach is considered.
Sensitivity to perturbations of a time-reversed acoustic wave in a multiple scattering medium Tourin, A., A. Derode, and M. Fink Physical Review Letters 87, no. 27 I, 2743011-2743014 (2001) Résumé: Analysis of experimental results on the robustness of acoustic focusing in a multiple scattering medium undergoing perturbations was presented. A time reversal experiment was performed to follow its time-dependent evolution in a perturbed random medium. The method was found to be analogous to the diffusive acoustic wave spectroscopy developed to study fluidized suspensions of particles. Mots-clés: Optical correlation; Perturbation techniques; Scattering; Sensitivity analysis; Spectroscopic analysis; Transducers; Diffusive wave spectroscopy; Multiple scattering; Ultrasonic waves
Generation of very high pressure pulses with 1-bit time reversal in a solid waveguide Montaldo, G., P. Roux, A. Derode, C. Negreira, and M. Fink Journal of the Acoustical Society of America 110, no. 6, 2849-2857 (2001) Résumé: The use of piezoelectric transducer arrays has opened up the possibility of electronic steering and focusing of acoustic beams to track kidney stones. However, owing to the limited pressure delivered by each transducer (typically 10 bar), the number of transducers needed to reach an amplitude at the focus on the order of 1000 bars is typically of some hundreds of elements. We present here a new solution based on 1-bit time reversal in a solid waveguide to obtain, with a small number of transducers, a very high amplitude pulse in tissues located in front of the waveguide. The idea is to take advantage of the temporal dispersion in the waveguide to create, after time reversal, a temporally recompressed pulse with a stronger amplitude. The aim of this work is threefold: first, we experimentally demonstrate 1-bit time reversal between a point source in water and several transducers fastened to one section of a finite-length cylindrical waveguide. Second, we numerically and experimentally study the temporal and spatial focusing at the source as a function of the characteristics of the "solid waveguide-time reversal mirror (TRM)" system: length and diameter of the guide, number of transducers of the TRM. Last, we show that the instantaneous power delivered in water at the focus of the solid waveguide is much higher than the power directly transmitted into water from a classically focused transducer. The combination of 1-bit time reversal and a solid waveguide leads to shock wave lithotripsy with low-power electronics. © 2001 Acoustical Society of America. Mots-clés: Arrays; Piezoelectric transducers; Shock waves; Steering; Waveguides; High pressure pulses; Lithotripsies; Acoustics; acoustic technique; pulse generator; acoustics; amplitude modulation; article; electronics; hyperbarism; lithotripsy; nephrolithiasis; pressure; priority journal; pulse generator; transducer; waveform
Observation of a coherent backscattering effect with a dipolar source for elastic waves: Highlight of the role played by the source De Rosny, J., A. Tourin, and M. Fink Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 64, no. 6 II, 066604/1-066604/4 (2001) Résumé: Experimental evidence of the role played by the source on the coherent backscattering effect (CBE) for elastic waves was established. It was shown that using a dipolar source and a monopolar receiver, a "bicone" can be obtained instead of a simple cone that is well explained by describing dipolar as the superposition of two monopolar sources opposite in phases. Mots-clés: Aluminum; Computational methods; Eigenvalues and eigenfunctions; Elastic waves; Fourier transforms; Interferometers; Lenses; Modal analysis; Optical beam splitters; Silicon; Transducers; Bicone; Chaotic cavity; Coherent backscattering effect; Heterodyne interferometer; Multipolar emitter-receiver; Pointlike dipolar source; Silicon plate; Backscattering
Numerical and experimental time-reversal of acoustic waves in random media Derode, A., M. Tanter, A. Tourin, L. Sandrin, and M. Fink Journal of Computational Acoustics 9, no. 3, 993-1003 (2001) Résumé: In classical mechanics, a time-reversal experiment with a large number of particles is impossible. Because of the high sensitivity to initial conditions, one would need to resolve the positions and velocities of each particle with infinite accuracy. Thus, it would require an infinite amount of information, which is of course out of reach. In wave physics however, the amount of information required to describe a wave field is limited and depends on the shortest wavelength of the field. Thus we can propose an acoustic equivalent of the experiment we mentioned above. We start with a coherent transient pulse, let it propagate through a disordered highly scattering medium, then record the scattered field and time-reverse it: surprisingly, it travels back to its initial source, which is not predictable by usual theories for random media. Indeed, to study waves propagation in disordered media theoreticians, who find it difficult to deal with one realization of disorder, use concepts defined as an average over the realizations, which naturally leads to the diffusion approximation. But the corresponding equation is not time-reversal invariant and thus fails in describing our experiment. Then, to understand our experimental results and try to predict new ones, we have developed a finite elements simulation based on the real microscopic time-invariant equation of propagation. The experimental and numerical results are found to be in very good agreement.
Ultrasound propagation through a rotational flow: Numerical methods compared to experiments Manneville, S., C. Prada, M. Tanter, M. Fink, and J.-F. Pinton Journal of Computational Acoustics 9, no. 3, 841-852 (2001) Résumé: Sound propagation through a vortex is studied numerically using two different techniques: ray-tracing and finite-differences. Geometrical acoustics and ray-tracing are shown to yield a good picture of the interaction between a sound wave and a vortex when the ratio of the vortex radius to the acoustic wavelength is larger than one. In particular, this technique allows to take into account finite-size effects such as edge waves and the results are compared to experimental data. The interest of the finite-difference approach is demonstrated for cases where sound scattering occurs. We show the ability of such a simulation to account for both sound scattering and finite-size effects. Those two numerical techniques are compared and their validity is investigated.
Random multiple scattering of ultrasound. II. Is time reversal a self-averaging process? Derode, A., A. Tourin, and M. Fink Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 64, no. 3 II, 366061-366113 (2001) Résumé: The statistical moments of ultrasonic waves transmitted through a disordered medium with resonant multiple scattering were investigated. An ultrasonic pulsed wave was transmitted from a point source to a 128-element receiving array through two-dimensional samples with various thickness. The results show that a robust estimation on a single realization of disorder is obtained using wide frequency bandwidth. Mots-clés: Acoustic wave propagation; Backscattering; Bandwidth; Integral equations; Interfaces (computer); Mathematical models; Piezoelectric devices; Steel; Ultrasonic scattering; Ultrasonic pulsed waves; Ultrasonic waves
Random multiple scattering of ultrasound. I. Coherent and ballistic waves Derode, A., A. Tourin, and M. Fink Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 64, no. 3 II, 366051-366057 (2001) Résumé: Random multiple scattering of ultrasound was analyzed using statistical approach techniques. An ultrasonic pulsed wave transmitted from a point source to a 128-element receiving array was studied through two dimensional samples with various thickness. It is found that the transmitted wave forms exhibits a time-dependent frequency spectrum. The results show that the secondary wave forms on the coherent wave form is produced due to the presence of elastic resonance in the given frequency bandwidth. Mots-clés: Backscattering; Ballistics; Coherent light; Integral equations; Mathematical models; Ultrasonic scattering; Ballistic waves; Resonant multiple scattering; Ultrasonic waves
Optimal focusing by spatio-temporal inverse filter. I. Basic principles Tanter, M., J.-F. Aubry, J. Gerber, J.-L. Thomas, and M. Fink Journal of the Acoustical Society of America 110, no. 1, 37-47 (2001) Résumé: A focusing technique based on the inversion of the propagation operator relating an array of transducers to a set of control points inside a medium was proposed in previous work [Tanter et al., J. Acoust. Soc. Am. 108, 223-234 (2000)] and is extended here to the time domain. As the inversion of the propagation operator is achieved both in space and time, this technique allows calculation of the set of temporal signals to be emitted by each element of the array in order to optimally focus on a chosen control point. This broadband inversion process takes advantage of the singular-value decomposition of the propagation operator in the Fourier domain. The physical meaning of this decomposition is explained in a homogeneous medium. In particular, a definition of the number of degrees of freedom necessary to define the acoustic field generated by an array of limited aperture in a focal plane of limited extent is given. This number corresponds to the number of independent signals that can be created in the focal area both in space and time. In this paper, this broadband inverse-focusing technique is compared in homogeneous media with the classical focusing achieved by simple geometrical considerations but also with time-reversal focusing. It is shown that, even in a simple medium, slight differences appear between these three focusing strategies. In the companion paper [Aubry et al., J. Acoust. Soc. Am. 1107 48-58 (2001)] the three focusing techniques are compared in heterogeneous, absorbing, or complex media where classical focusing is strongly degraded. The strong improvement achieved by the spatio-temporal inverse-filter technique emphasizes the great potential of multiple-channel systems having the ability to apply completely different signal waveforms on each transducer of the array. The application of this focusing technique could be of great interest in various ultrasonic fields such as medical imaging, nondestructive testing, and underwater acoustics. © 2001 Acoustical Society of America. Mots-clés: Acoustic arrays; Acoustic fields; Decomposition; Degrees of freedom (mechanics); Transducers; Ultrasonics; Waveform analysis; Spatio-temporal inverse filters; Acoustic transducers; filter; article; comparative study; frequency modulation; priority journal; signal processing; simulation; sound transmission; spatial frequency discrimination; ultrasound transducer; Echoencephalography; Filtration; Fourier Analysis; Humans; Phantoms, Imaging; Transducers; Ultrasonography
Optimal focusing by spatio-temporal inverse filter. II. Experiments. Application to focusing through absorbing and reverberating media Aubry, J.-F., M. Tanter, J. Gerber, J.-L. Thomas, and M. Fink Journal of the Acoustical Society of America 110, no. 1, 48-58 (2001) Résumé: To focus ultrasonic waves in an unknown heterogeneous medium using a phased array, one has to calculate the optimal set of signals to be applied on the transducers of the array. (In most applications of ultrasound, medical imaging, medical therapy, nondestructive testing, the first step consists of focusing a broadband ultrasound beam deeply inside the medium to be investigated.) Focusing in a homogeneous medium simply requires to compensate for the varying focus-array elements geometrical distances. Nevertheless, heterogeneities in the medium, in terms of speed of sound, density, or absorption, may strongly degrade the focusing. Different techniques have been developed in order to correct such aberrations induced by heterogeneous media (time reversal, speckle brightness, for example). In the companion to this paper, a new broadband focusing technique was investigated: the spatio-temporal inverse filter. Experimental results obtained in various media, such as reverberating and absorbing media, are presented here. In particular, intraplate echoes suppression and high-quality focusing through a human skull, as well as hyper-resolution in a reverberating medium, will be shown. It is important to notice that all these experiments were performed with fully programmable multichannel electronics whose use is required to fully exploit the spatio-temporal technique. © 2001 Acoustical Society of America. Mots-clés: Absorption; Acoustic arrays; Echo suppression; Reverberation; Ultrasonic waves; Spatio-temporal inverse filters; Acoustic transducers; filter; amplifier; article; density; electronics; priority journal; signal processing; sound transmission; spatial frequency discrimination; ultrasound transducer; Echoencephalography; Filtration; Fourier Analysis; Humans; Phantoms, Imaging; Software; Transducers; Ultrasonic Therapy; Ultrasonography
Ultrasonic imaging using spatio-temporal matched field (STMF) processing-applications to liquid and solid waveguides Ing, R. K., and M. Fink IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 48, no. 2, 374-386 (2001) Résumé: This paper is devoted to imaging defects in liquid and solid ultrasonic waveguides. A new ultrasonic imaging technique, based on the spatio-temporal Green functions computation and cross-correlation, is presented. This technique extends the concept of matched field processing (MFP) used in ocean acoustics. Results of experiments conducted in water and in a solid Duralumin bar show that a strong improvement of the spatial resolution is observed with this MFP. Mots-clés: Approximation theory; Computer simulation; Green's function; Oceanography; Ultrasonic transmission; Ultrasonic waves; Waveguides; Duralumin bar; Ocean acoustics; Spatio-temporal matched field processing; Ultrasonic imaging
Time-resolved 2D pulsed elastography. Experiments on tissue-equivalent phantoms and breast in-vivo Sandrin, L., M. Tanter, S. Catheline, and M. Fink Proceedings of SPIE - The International Society for Optical Engineering 4325, 120-126 (2001) Résumé: Time-Resolved 2D Pulsed Elastography is a new elastographic technique for imaging the shear modulus of soft tissues. A low-frequency transient shear wave is sent in the medium while an ultra-fast ultrasonic imaging system acquires frames at a very high frame rate (up to 10,000 frames/s). This ultra-fast ultrasonic imaging system has been specifically developed for this application. It is based on a time-reversal mirror of 128 channels sampled at 50 MHz and having 2 Mbytes random access memory. Displacements induced by the slowly propagating shear wave are measured using the standard cross-correlation technique. The low-frequency excitation is obtained with a device composed of two rods that are placed around the ultrasonic transducer linear array. The rods vibrate perpendicularly to the surface of the tissues. They may be either parallel or perpendicular to the active surface of the array. With this device, large amplitude displacements are observed in the ultrasonic image area. We have measured the spatio-temporal evolution of the displacements induced by the low-frequency (20-100 Hz) shear wave in tissue-equivalent phantoms and breast in-vivo. A direct local inversion is used to recover the shear modulus distribution map in phantoms containing hard regions. Mots-clés: Elastography; High frame rate imaging; Inversion algorithm; Shear modulus; Shear wave; Soft tissues; Transient; Algorithms; Elastic moduli; Image reconstruction; Imaging systems; Shear waves; Tissue; Transients; Ultrasonic transducers; Elastography; Medical imaging
Multiple scattering of sound Tourin, A., M. Fink, and A. Derode Waves Random Media 10, no. 4, R31-R60 (2000) Résumé: We present a topical review which summarizes the main contributions to `multiple scattering of acoustic and elastic waves' including the most recent advances.The review is divided into five main parts.In the first part, the effects of multiple scattering on ultrasonic propagation are illustrated on the basis of three experimental examples.In the second and third parts, we present the two possible descriptions for the propagation of an acoustic wave in a random medium. The first one is based on the study of the coherent wave, i.e. the wave amplitude averaged over disorder, whereas the second one deals with the propagation of the incoherent intensity, i.e. the intensity averaged over disorder. We especially insist on the microscopic basis for the phenomenological radiative transfer equation and show how it can be solved in the diffusion approximation. The theory is illustrated with experimental results obtained on a two-dimensional multiple-scattering prototype made of thousands of steel rods randomly distributed and immersed in water. In the fourth part, we present experimental evidence that the diffusion equation fails in describing all the aspects of the propagation of an acoustic wave in a random medium: e.g. the coherent backscattering effect recently observed for ultrasonic waves. We show that this effect arises as a consequence of reciprocity. Finally, in the fifth part, we discuss another property which is not taken into account in the radiative transfer theory: the reversibility of an acoustic wave propagating in a disordered medium. Mots-clés: Acoustic wave backscattering; Approximation theory; Diffusion; Mathematical models; Ultrasonic propagation; Coherent backscattering effects; Radiative transfer equation; Acoustic wave scattering
Transport parameters for an ultrasonic pulsed wave propagating in a multiple scattering medium Tourin, A., A. Derode, A. Peyre, and M. Fink Journal of the Acoustical Society of America 108, no. 2, 503-512 (2000) Résumé: A set of ultrasonic experimental methods was developed to characterize a multiple scattering medium in terms of l(s), l*, l(a), respectively, the elastic, transport, and absorption mean free paths and D the diffusion constant. Actually, these quantities are the key parameters for a wave propagating in a disordered medium. Although they are widely used in optics, they are less common in acoustics. The underlying model is based on the expansion of the average solution for the heterogeneous Green's function equation. To validate this theoretical approach, a sample made of randomly located steel rods was used as a prototype. Through time-resolved measurements of the transmitted amplitude, the difference between the ballistic and the coherent wave is highlighted. In varying the sample thickness, l(s) is determined, the coherent and diffusive regime are distinguished, and the transition from one to the other is followed. Furthermore, as a limit to a description of the average intensity based on the diffusion approximation, the existence of a coherent backscattering effect is shown. This latter gives a method to estimate D and l*. These quantities being determined, it becomes possible to infer l(a) using average time-resolved intensity measurements. Finally, some applications to coarse-grain stainless steels are discussed. (C) 2000 Acoustical Society of America. Mots-clés: acoustics; article; calculation; mathematical analysis; priority journal; sound; theory; ultrasound
Time reversal and the inverse filter Tanter, M., J.-L. Thomas, and M. Fink Journal of the Acoustical Society of America 108, no. 1, 223-234 (2000) Résumé: To focus ultrasonic waves in an unknown inhomogeneous medium using a phased array, one has to calculate the optimal set of signals to be applied on the transducers of the array. In the case of time-reversal mirrors, one assumes that a source is available at the focus, providing the Green's function of this point. In this paper, the robustness of this time-reversal method is investigated when loss of information breaks the time-reversal invariance. It arises in dissipative media or when the field radiated by the source is not entirely measured by the limited aperture of a time-reversal mirror. However, in both cases, linearity and reciprocity relations ensure time reversal to achieve a spatiotemporal matched filtering. Nevertheless, though it provides robustness to this method, no constraints are imposed on the field out of the focus and sidelobes may appear. Another approach consists of measuring the Green's functions associated to the focus but also to neighboring points. Thus, the whole information characterizing the medium is known and the inverse source problem can be solved. A matrix formalism of the propagation operator is introduced to compare the time-reversal and inverse filter techniques. Moreover, experiments investigated in various media are presented to illustrate this comparison. (C) 2000 Acoustical Society of America. Mots-clés: Fourier transformation; priority journal; review; time; transducer; ultrasound; Humans; Models, Theoretical; Skull; Time
Limits of time-reversal focusing through multiple scattering: Long-range correlation Derode, A., A. Tourin, and M. Fink Journal of the Acoustical Society of America 107, no. 6, 2987-2998 (2000) Résumé: Experimental results of time-reversal focusing in a high-order multiple scattering medium are presented and compared to theoretical predictions based on a statistical model. The medium consists of a random collection of parallel steel rods. An ultrasonic source (3.2 MHz) transmits a pulse that undergoes multiple scattering and is recorded on an array. The time-reversed waves are sent by the array back to the source through the scattering medium. The quality of temporal focusing is very well predicted by a simple statistical model. However, for thicker samples, persistent temporal side- lobes appear. We interpret these side-lobes as a consequence of the growing number of crossing paths in the sample due to high-order multiple scattering. As to spatial focusing, the resolution is practically independent from the array's aperture. With a 16-element array, the resolution was found to be 30 times finer than in a homogeneous medium. Resolutions of the order of the wavelength (0.5 mm) were attained. These results are discussed in relation with the statistical properties of time-reversal mirrors in a random medium. (C) 2000 Acoustical Society of America. Mots-clés: acoustics; article; priority journal; signal noise ratio; signal transduction; sound transmission; statistical analysis; thickness
Time reversal in a waveguide: Study of the temporal and spatial focusing Roux, P., and M. Fink Journal of the Acoustical Society of America 107, no. 5 I, 2418-2429 (2000) Résumé: Temporal and spatial focusing properties of time-reversal mirrors (TRMs) are studied in a waveguide. The experiments are done using an ultrasonic TRM in an idealized waveguide. The width of the focal spot, and the spatial and temporal sidelobe levels are experimentally and numerically analyzed with respect to the characteristics of the waveguide-TRM system. An algorithm is developed to compute directly in the time domain the time-reversed field. This algorithm is based on the application of the mirror theorem to both the source and the TRM placed in the waveguide. Because time reversal is a stable and robust process, some of the ultrasonic results can be extended to ocean acoustics. Applications to underwater acoustic transmissions as well as ultrasonic medical imaging are discussed. (C) 2000 Acoustical Society of America. Mots-clés: acoustics; algorithm; amplitude modulation; article; imaging; mathematical computing; priority journal; sound transmission; ultrasound
Coherent Backscattering of an Elastic Wave in a Chaotic Cavity De Rosny, J., A. Tourin, and M. Fink Physical Review Letters 84, no. 8, 1693-1695 (2000) Résumé: We report the first experimental evidence of coherent backscattering enhancement for transient elastic waves propagating in a two-dimensional chaotic cavity. The time-integrated squared amplitude at the point source is twice as large as at the other points around the source. Contrary to analogous optical experiments, this effect is already clearly observable on a single realization. Especially, the spatial shape of the coherent backscattering enhancement is well predicted by a generalization of the existing theory.
Time-reversal mirrors and rough surfaces: Experiment Roux, P., J. De Rosny, M. Fink, and J. H. Rose Journal of the Acoustical Society of America 106, no. 2, 724-732 (1999) Résumé: A novel acoustic time-reversal technique has been tested for determining the surface-height autocorrelation function and rms height of rough surfaces. A time-reversal mirror (TRM) was used to insonify periodically and 'randomly' rough surfaces of otherwise flat samples immersed in water. The standard use of the TRM is as follows: transmit an initial planar pulse, record the signals at each array element, digitally time reverse each signal, and then retransmit the time-reversed signal. As expected from time-reversal symmetry, one approximately recovers the incident planar pulse after the reflection of the retransmitted wave. The new technique is a simple modification of this procedure. Namely, as before, we record and time reverse the initial reflection. However, we next translate the transducer a fixed distance parallel to the surface before retransmitting. For very small displacements, little change is observed in the TRM's signal. For larger and larger translations, the TRM's signal decorrelates, i.e., it less and less resembles the incident pulse. The signal's decorrelation as a function of displacement is directly related to the autocorrelation function of the rough surface within the limits set by the system's point response function. The TRM was used both in reflection mode and in transmission mode. Samples consisted of 'randomly' rough surfaces of metal and plastic plates, as well as metal plates machined to have periodically rough surfaces. Evidence is provided that the time-reversal mirror is sensitive to the surface-height autocorrelation and, in favorable cases, determines the autocorrelation function and rms height. Mots-clés: acoustics; article; geometry; measurement; physical parameters; priority journal; sound transmission; ultrasound
Time-reversal mirrors and rough surfaces: Theory Rose, J. H., M. Bilgen, P. Roux, and M. Fink Journal of the Acoustical Society of America 106, no. 2, 716-723 (1999) Résumé: A systematic study is presented of the sensitivity of acoustic time- reversal mirrors (TRMs) to errors. One result is a novel acoustic method for determining the root-mean-square, rms, height and the surface-height autocorrelation function of rough surfaces. In particular, the effects of misregistering a TRM are studied with respect to a rough surface the reflected wavefield is recorded in one place, time reversed, and then rebroadcast in a second place. This displacement causes the signal to depend importantly on the surface's rms height and autocorrelation function. Simple closed-form formulas are presented for determining the rms height and the normalized surface-height autocorrelation function for both deterministic and randomly rough surfaces. Also presented is a numerical study that illustrates the statistical uncertainty in and the spatial resolution of the proposed method. An accompanying experimental article tests the proposed method with measurements made on a number of different rough surfaces. Mots-clés: acoustics; article; measurement; physical parameters; priority journal; sound; statistical model; theory
Dynamic time reversal of randomly backscattered acoustic waves Tourin, A., A. Derode, and M. Fink Europhysics Letters 47, no. 2, 175-181 (1999) Résumé: We report the first experiments using the reversibility of a transient acoustic wave in a multiple-scattering medium to simulate either a stationary or a dynamic acoustic lens. The method is based on time reversal experiments performed in a backscattering configuration. In the stationary case, we show that we take advantage of multiple scattering to focus better than with a perfect reflecting interface. In the dynamic case, we explain the refocused spot time evolution by a simple model based on the time-dependent ability to recover the angular spectrum thanks to both single- and multiple-scattering paths.
Characterization of a large vortex using acoustic time-reversal mirrors Manneville, S., A. Maurel, P. Roux, and M. Fink European Physical Journal B 9, no. 3, 545-549 (1999) Résumé: We report new results on the ultrasonic characterization of a fluid flow using an acoustic time-reversal mirror (TRM). The structure of a large vortex generated by a rotating disk in a hollow cylinder is investigated both inside and below the cylinder. For mean-flow characterization, the TRM is shown to be a powerful vorticity detector. Experimental time-of-flight data are successfully compared to a numerical simulation of the flow and the orthoradial velocity is reconstructed using simple geometrical acoustics. Realtime measurements allow us to extract the precession motion of the vortex, providing direct, non-intrusive, and dynamical information on the flow. Mots-clés: 43.30+m underwater sound; 43.35+d ultrasonics, quantum acoustics, and physical effects of sound; 47.32-y rotational flow and vorticity
Ultrasound puts materials to the test Fink, M. Physics World 11, no. 2, 41-45 (1998)
Acoustic time reversal with mode conversion at a solid-fluid interface Draeger, C., D. Cassereau, and M. Fink Applied Physics Letters 72, no. 13, 1567-1569 (1998) Résumé: Acoustic time-reversal experiments are mostly carried out in fluid media. This letter presents experiments proving the capability of a time-reversal mirror to obtain simultaneous focusing of both propagation modes inside a solid. The mirror is located in a surrounding fluid and records the longitudinal and transverse wavefronts (created by a laser impact on the solid) after conversion into pressure waves at the solid-fluid interface. We show that the time-reversed pressure wavefronts are reconverted mostly to their original propagation mode and focus simultaneously at the location of the laser impact. © 1998 American Institute of Physics.
Influence of boundary conditions on time-reversal focusing through heterogeneous media Tanter, M., J.-L. Thomas, and M. Fink Applied Physics Letters 72, no. 20, 2511-2513 (1998) Résumé: This letter presents a way to overcome ultrasonic focusing degradations through strongly diffracting nondissipative layers. A first set of experiments shows that, using finite aperture transducer arrays, neither the time-reversal technique, nor other focusing techniques are able to achieve proper focusing through this kind of aberrator. These experimental results show the limits of a finite aperture time-reversal mirror compared to the theoretical behavior of a time-reversal cavity. To simulate a time-reversal cavity, totally reflecting walls are set between the time-reversal mirror and the aberrator. The experiments and numerical simulations presented in this letter show that as soon as we introduce these reflecting boundaries, the time-reversal focusing becomes optimal and the spatial resolution is strongly improved. © 1998 American Institute of Physics.
Focusing and steering through absorbing and aberrating layers: Application to ultrasonic propagation through the skull Tanter, M., J.-L. Thomas, and M. Fink Journal of the Acoustical Society of America 103, no. 5 I, 2403-2410 (1998) Résumé: The time-reversal process is applied to focus pulsed ultrasonic waves through the human skull bone. The aim here is to treat brain tumors, which are difficult to reach with classical surgery means. Such a surgical application requires precise control of the size and location of the therapeutic focal beam. The severe ultrasonic attenuation in the skull reduces the efficiency of the time reversal process. Nevertheless, an improvement of the time reversal process in absorbing media has been investigated and applied to the focusing through the skull [J.-L. Thomas and M. Fink, IEEE Trans. Ultrason. Ferroelectr. Freq. Control 43, 1122-1129 (1996)]. Here an extension of this technique is presented in order to focus on a set of points surrounding an initial artificial source implanted in the tissue volume to treat. From the knowledge of the Green's function matched to this initial source location a new Green's function matched to various points of interest is deduced in order to treat the whole volume. In a homogeneous medium, conventional steering consists of tilting the wave front focused on the acoustical source. In a heterogeneous medium, this process is only valid for small angles or when aberrations are located in a layer close to the array. It is shown here how to extend this method to aberrating and absorbing layers, like the skull bone, located at any distance from the array of transducers. Mots-clés: article; brain surgery; human; mathematical analysis; priority journal; signal transduction; skull; skull surgery; ultrasound; Brain Neoplasms; Humans; Models, Biological; Skull; Ultrasonic Therapy; Ultrasonics
Time reversal in multiply scattering media Derode, A., A. Tourin, and M. Fink Ultrasonics 36, no. 1-5, 443-447 (1998) Résumé: The application of time-reversal mirrors (TRM) to media with very high-order multiple scattering is presented. Random sets of up to 2500 steel rods are considered. When a pulsed wave traverses such a medium, it undergoes many scatterings before reaching the TRM. The resulting pressure field spreads in time, up to 300 times the initial pulse duration; it is recorded, time-reversed and retransmitted through the same disordered medium. Surprisingly, the time-reversed waves are found to converge to their source and recover their original waveform and duration, unlike one could have expected given the high order of multiple scattering involved and the usual sensitivity to initial conditions of time-reversal processes. In addition to this, the observed resolution of the time-reversed waves was greatly increased, and found to be smaller than the theoretical limit for the array's aperture. Theoretical limits of time-reversed experiments are discussed. © 1998 Elsevier Science B.V. Mots-clés: Multiple scattering; Time reversal; Steel; Ultrasonic transmission; Ultrasonics; Time reversal mirrors (TRM); Ultrasonic scattering
Correlation length of ultrasonic speckle in anisotropic random media: Application to coherent echo detection Derode, A., and M. Fink Journal of the Acoustical Society of America 103, no. 1, 73-82 (1998) Résumé: In a recent paper [Derode and Fink, J. Acoust. Soc. Am. 101, 690-704 (1997)], a technique for studying spatial coherence properties of backscattered speckle noise by means of a transducers array was described. In this paper another approach is presented. Here, a single transducer, focusing inside a scattering medium, is moved in a plane; correlation is studied between signals acquired in two different positions. A study investigates how the correlation function of the medium determines that of the speckle noise This is applied to fully or partially incoherent media, and media with anisotropic scatterer distribution such as unidirectional and cross-ply composites; we show that it is possible to extract information about the medium from a measurement of the backscattered field correlation length. The influence of correlation length on defect detection is discussed. Experimental as well as theoretical results are presented, they are found in good agreement. Mots-clés: anisotropy; article; correlation function; echography; fourier transformation; noise; priority journal; sound detection; sound transmission; ultrasound; ultrasound transducer
Aberration correction in ultrasonic medical imaging with time-reversal techniques Fink, M., and C. Dorme International Journal of Imaging Systems and Technology 8, no. 1, 110-125 (1997) Résumé: Degradation of image quality is currently observed with ultrasonic scanners owing to distortion of the ultrasonic beams through inhomogeneous tissue layers. Adaptive time-delay focusing techniques allow an efficient correction of these effects when the inhomogeneous layer is close to the transducer array. If the aberrating layers are far from the array, these techniques are no longer appropriate to correct the propagation effects between the layer and the transducer array. In this article we show that time-reversal mirrors can solve this problem. In the matched-filter approach that extends the concept of time reversal mirrors, the Green's function of a dominant scatterer available in the medium is recorded in digital memory and used to focus on the scatterer in both transmit and receive modes. An extension of this technique is also presented to focus, in the presence of an aberrating layer, not only on the dominant scatterer, but also around it to image the surrounding zone. From the knowledge of the Green's function needed to focus on the initial scatterer, new Green's functions matched to the new point of interest are calculated. The algorithm uses the concept of time-reversal propagation, and theoretical and experimental results obtained with this technique are presented. The calculation of each Green's function matched to each new desired focal point allows us to realize a B-scan image of the zone surrounding the reflector. © 1997 John Wiley & Sons, Inc. Mots-clés: Aberration correction; Beam forming; Matched filter; Medical imaging; Time reversal; Ultrasound; Aberrations; Algorithms; Green's function; Image quality; Medical imaging; Mirrors; Aberration correction; Beam forming; Matched filter; Time reversal mirrors; Ultrasonic imaging
Partial coherence of transient ultrasonic fields in anisotropic random media: Application to coherent echo detection Derode, A., and M. Fink Journal of the Acoustical Society of America 101, no. 2, 690-704 (1997) Résumé: In this paper the spatial coherence properties of the speckle noise backscattered from random media insonified by a broadband pulse are studied. The approach presented is an adaptation of the optical notion of coherence introduced by Zernike. How the statistical parameters (particularly the second-order moment) of the medium determine those of the speckle noise is studied. This is applied to fully or partially incoherent media, and media with anisotropic scatterer distribution such as unidirectional and cross-ply composites; also investigated is the possibility of detecting a coherent reflector among speckle noise through measurements of coherence length. Experimental as well as theoretical results are presented. Measurements were carried out with a linear array of 128 programmable transmitters/receivers. Mots-clés: acoustics; anisotropy; article; fourier transformation; noise; priority journal; statistical parameters; transducer; ultrasound
Ultrasonic beam steering through inhomogeneous layers with a time reversal mirror Dorme, C., and M. A. Fink IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 43, no. 1, 167-175 (1996) Résumé: Adaptive time delay focusing techniques allow an efficient correction of the effects due to an inhomogeneous layer close to the transducer array. If the layer is far from the array, these techniques are no longer appropriate to correct the diffraction effects between the layer and the transducer array. This problem was overcome by the use of acoustic time reversal mirrors [1J. In this technique, the Green's function of a dominant scatterer available in the medium is recorded in digital memories and used to focus on the scatterer in both transmit and receive modes [2]. We present in this paper an extension of this technique to focus, in the presence of an aberrating layer, not only on the dominant scatterer, but also around it in order to image the surrounding zone. From the knowledge of the Green's function needed to focus on the initial scatterer, we calculate the new Green's function matched to the new point of interest. The algorithm uses the concept of time reversal propagation, and we shall present here theoretical and experimental results obtained with this technique. Finally, the knowledge of each Green's function matched to each new desired focal point allows the realization of a B-scan image of the zone surrounding the reflector. © 1996 IEEE. Mots-clés: Aberrations; Algorithms; Calculations; Data storage equipment; Focusing; Green's function; Mirrors; Ultrasonic diffraction; Ultrasonic propagation; Ultrasonic scattering; Ultrasonic transducers; Aberrating layer; Adaptive time delay focusing technique; B scan image; Inhomogeneous layers; Time reversal mirror; Transducer array; Ultrasonic beam steering; Ultrasonic reflection
Self-focusing Rayleigh wave using a time reversal mirror Ing, R. K., M. Fink, and O. Casula Applied Physics Letters 68, no. 2, 161-163 (1996) Résumé: Detection of surface and subsurface flaws is achieved using the time reversal process leading to self-focusing Rayleigh waves. The generation of surface waves is accomplished with an array of transducers coupled to the specimen with a Plexiglas wedge. The advantages of this technique are demonstrated with the detection of surface and subsurface holes of subwavelength dimensions. An optical interferometer is used to control the surface acoustic field obtained with such a time reversal process. © 1996 American Institute of Physics. Mots-clés: Acoustic arrays; Acoustic transducers; Acoustic wave propagation; Acoustic waves; Boundary conditions; Focusing; Interferometers; Mirrors; Signal detection; Surfaces; Optical interferometer; Plexiglass wedge; Rayleigh waves; Self focusing; Subsurface flaw; Surface acoustic field; Surface flaw; Time reversal; Surface waves
Time reversal focusing applied to lithotripsy Thomas, J.-L., F. Wu, and M. Fink Ultrasonic Imaging 18, no. 2, 106-121 (1996) Résumé: Time reversal of ultrasonic field allows a very efficient approach to focusing pulsed ultrasonic waves through lossless inhomogeneous media. Time reversal mirrors (TRM) are made of large transducer arrays, allowing the incident acoustic field to be sampled, time reversed and re-emitted. Time reversal processing permits a choice of any temporal window to be time reversed, allowing operation in an iterative mode. In multitarget media, this process converges on the most reflective target, i.e., the dominant scatterer. In this paper, the time reversal process is applied to track, in real time, a moving gall bladder or kidney stone embedded in its surrounding medium. We investigate the feasibility of a piezoelectric shock wave generator in which the focal zone is moved electronically to track the stone during a lithotripsy treatment. We show that TRM allows us to obtain sharp focusing on one bright point of the stone. The time of flight profile is then determined and used in a least-mean-square method to calculate the spatial coordinates of the stone. Mots-clés: Electronic focusing, extrapolation; lithotripsy; piezoelectric generator; stone tracking; time delay estimation; time reversal mirrors; ultrasound; article; cholelithiasis; lithotripsy; piezoelectricity; shock wave; time; ultrasound; Cholelithiasis; Humans; Kidney Calculi; Lithotripsy; Ultrasonography, Interventional
Self-focusing Rayleigh wave using a time reversal mirror Ing, R. K., M. Fink, and O. Casula Applied Physics Letters, 161 (1995) Résumé: Detection of surface and subsurface flaws is achieved using the time reversal process leading to self-focusing Rayleigh waves. The generation of surface waves is accomplished with an array of transducers coupled to the specimen with a Plexiglas wedge. The advantages of this technique are demonstrated with the detection of surface and subsurface holes of subwavelength dimensions. An optical interferometer is used to control the surface acoustic field obtained with such a time reversal process. © 1996 American Institute of Physics.
The iterative time reversal process: Analysis of the convergence Prada, C., J.-L. Thomas, and M. Fink Journal of the Acoustical Society of America 97, no. 1, 62-71 (1995) Résumé: The efficiency of a time reversal acoustic mirror to focus on a reflective target through an inhomogeneous media has been demonstrated. In a multitarget media, the ability of such a mirror to work in an iterative mode in order to focus selectively on the strongest target was shown [C. Prada, F. Wu, and M. Fink, J. Acoust. Soc. Am. 90, 1119 (1991)]. The theory of how the iterative time reversal process is built is based on a matrix formalism and treats the array of L transducers in a given medium as a linear system of L inputs/L outputs. The system is characterized at each frequency by its transfer matrix K and the time reversal iterative process is then described by a time reversal operator K*K. Because of the reciprocity principle, this operator is Hermitian. The following result is shown: If the scattering medium is a set of well resolved targets of different reflectivities then each eigenvector of the operator K*K with nonzero eigenvalue corresponds to one of the targets in the set and provides the optimum phase law to focus on it. Furthermore, the eigenvalue is proportional to the reflectivity of the target. In particular, the 'brightest' target is associated to the eigenvector of greatest eigenvalue so that the iterative time reversal process leads to a wave focusing on this target. This analysis is illustrated by numerical and experimental results. Mots-clés: acoustics; article; brightness; mathematical analysis; priority journal; signal transduction; sound; surface property; waveform; acoustic transducers; convergence; experimental study; iterative time reversal
Inverse scattering analysis with an acoustic time-reversal mirror Thomas, J.-L., P. Roux, and M. Fink Physical Review Letters 72, no. 5, 637-640 (1994) Résumé: Time-reversal mirror (TRM) utilizes time-reversal invariance of wave equation. Acoustic TRM are made of large transducer arrays allowing the incident acoustic field to be sampled, time reversed, and reemitted. The ability of TRM to time reverse separately each scattered wave permits us to isolate spatially and temporally the equivalent sources of extended scatterer illuminated by broadband pulse. We investigate more particulary the problem of a cylindrical scatterer: We show that TRM allows us to determine the location of the mode conversions of incident waves into circumferential waves. © 1994 The American Physical Society.
Transient elastic wave generation by an array of thermoelastic sources Noroy, M.-H., D. Royer, and M. Fink Applied Physics Letters 63, no. 24, 3276-3278 (1993) Résumé: A set of 16 thermoelastic strip sources, equivalent to a phased array of ultrasonic transducers has been implemented on a solid by irradiating its surface with a multiple beam pulsed YAG laser. Longitudinal elastic waves were focused in the sample by time delaying each laser pulse. Results of experiments performed on duraluminum in the thermoelastic regime are presented and compared with simulations based on the surface center of the expansion model. It is shown that with this technique, a high energy focusing, together with an ultrasonic beam scanning can be achieved in a wide angular range leading to a significant improvement in the signal-to-noise ratio of a laser based ultrasonic system.
Optical probing of pulsed, focused ultrasonic fields using a heterodyne interferometer Royer, D., N. Dubois, and M. Fink Applied Physics Letters 61, no. 2, 153-155 (1992) Résumé: The pulsed acoustic field of a piezoelectric focused transducer transmitted in water has been investigated by using an optical heterodyne interferometer. The probe beam is reflected by a thin membrane that follows the motion of the fluid particle. Absolute measurements of the mechanical displacement have been performed in the frequency range 5-15 MHz with a spatial resolution better than 0.1 mm and a sensitivity of 0.1 nm with a 20 MHz detection bandwidth that corresponds to a minimum detectable acoustic energy density of 2 μJ/m 2. The experimental results all agree quantitatively with diffraction theory predictions of impulse response at the focus of the transducer.
The van Cittert-Zernike theorem in pulse echo measurements Mallart, R., and M. Fink Journal of the Acoustical Society of America 90, no. 5, 2718-2727 (1991) Résumé: A classical theorem of statistical optics, the van Cittert-Zernike theorem, is generalized to pulse echo ultrasound. This theorem fully describes the second-order statistics of the spatial fluctuations (the spatial covariance) of the field produced by an incoherent source. As a random scattering medium is insonified, it behaves as an incoherent source. The van Cittert-Zernike theorem can thus predict the spatial covariance of the pressure field backscattered by a random medium. It is shown that this spatial covariance and the incident energy diagram are Fourier pairs. In the case of a focused illumination, the spatial covariance of the backscattered pressure field is proportional to the autocorrelation of the transmitting aperture function. This is independent of frequency and of F/ number. Experimental results obtained with a linear array are in good agreement with theoretical expectations. The implications of this theorem in speckle reduction and in focusing in nonhomogenous media are discussed. Mots-clés: acoustics; article
The iterative time reversal mirror: A solution to self-focusing in the pulse echo mode Prada, C., F. Wu, and M. Fink Journal of the Acoustical Society of America 90, no. 2 I, 1119-1129 (1991) Résumé: Accurate focusing in an inhomogeneous medium is difficult to implement. In order to focus on a reflective target we have extended the concept of optical phase-conjugate mirrors, valid for monochromatic signals, to broadband pulses such as those used in ultrasound echography. The transducer's linear response to the acoustic pressure allows one to replace the phase conjugation by a time reversal operation on the pulse echo signals. The time reversal mirror is an array of transmit-receive transducers. A first incident wave is reflected by the target. The received signals are stored in shift registers, reversed in time, and then reemitted. The main advantage of this process is that waves distorted by the propagation through an aberrating medium are corrected by the mirror operation and the back propagation through the medium. When the medium contains several reflectors, this time reversal process can be iterated in order to focus on the most reflective one. Theoretical results on this principle, numerical simulations, and experimental results with a 1-D array working at a central frequency of 3 MHz are presented. Mots-clés: acoustics; article